https://github.com/FreeOpcUa/opcua-asyncio/issues/457

* Add method to add reverse references, if missing

* Replace NodeId numbers with ObjectIds
Fix bug - check if Node even has references, since a Node may be empty

* Fix wrong used Nodes to check

EffectiveTransitionTime will be reintroduced with the substatemachines

Use datetime.utcnow instead local now

Replace os with pathlib expressions
Make write process more visual

import datetime and change to utcnow() to be OPC UA conform

remove unused vars and comments
replace prints with logs

Make file write more elegant

indent formated strings in a Pep conform way
Replace os with pathlib expressions
Replace single quote with double quote
Replace multiple single lines with one string block

Get newest UA-Nodeset update from github
Remove old Nodesets
Generate new Nodesets

When a session has a short session timeout, the secure_channel is
renewed at 75% of it lifetime. While this is convenient to keep
the session alives, this might be an overkill in some situations
since the encryption involved behind the scene can be expensive,
specifically on hardware with limited resources (i.e: OPC-UA
server embedded on PLC module for example).

What I suggested here is to have more control over the secure channel
renewal and instead to rely on the subscription keepalive mechanism,
thus, the client won't timeout when subscriptions are inactive.
There's still the case when there's no subscription (client is
connected but idling), in this situation the user has to set a
secure_channel_timeout < session_timeout.

Finally, the library ua-server doesn't respect the session_timeout
sent by the client during session_creation. Probably worth to follow-up
on this.

Test with MaxKeepAliveCount == 22
(session_timeout = 30; publish_interval = 1000)
```
2021-02-07 16:23:00,147 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: CreateSubscriptionRequest(TypeId:i=787, RequestHeader:RequestHeader(AuthenticationToken:b=b'2\xd2\x82w\xad\x0f\x99\x9a %\xfaj\xb6\xb9\xaf\xa8\xe7\x13\xe6\xec\x15G\xf7G\x15\xbb\x82\x1d\xda\x17\xafh', Timestamp:2021-02-08 00:23:00.147523, RequestHandle:4, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:4000, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:CreateSubscriptionParameters(RequestedPublishingInterval:1000, RequestedLifetimeCount:10000, RequestedMaxKeepAliveCount:22, MaxNotificationsPerPublish:10000, PublishingEnabled:True, Priority:0))
2021-02-07 16:23:00,170 - asyncua.client.ua_client.UaClient - DEBUG - publish []
2021-02-07 16:23:00,170 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'2\xd2\x82w\xad\x0f\x99\x9a %\xfaj\xb6\xb9\xaf\xa8\xe7\x13\xe6\xec\x15G\xf7G\x15\xbb\x82\x1d\xda\x17\xafh', Timestamp:2021-02-08 00:23:00.170972, RequestHandle:6, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[]))
21-02-08 00:23:00.939388))], DiagnosticInfos:[])]), Results:[], DiagnosticInfos:[])
DataChangeNotification(<asyncua.common.subscription.SubscriptionItemData object at 0x7fdbf1444c10>, MonitoredItemNotification(ClientHandle:201, Value:DataValue(Value:Variant(val:300000,type:VariantType.Int32), StatusCode:StatusCode(Good), SourceTimestamp:2021-02-08 00:23:00.900000, ServerTimestamp:2021-02-08 00:23:00.939388)))

2021-02-07 16:23:01,189 - asyncua.client.ua_client.UaClient - DEBUG - publish [SubscriptionAcknowledgement(SubscriptionId:75, SequenceNumber:1)]
2021-02-07 16:23:01,189 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'2\xd2\x82w\xad\x0f\x99\x9a %\xfaj\xb6\xb9\xaf\xa8\xe7\x13\xe6\xec\x15G\xf7G\x15\xbb\x82\x1d\xda\x17\xafh', Timestamp:2021-02-08 00:23:01.189588, RequestHandle:7, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[SubscriptionAcknowledgement(SubscriptionId:75, SequenceNumber:1)]))
2021-02-07 16:23:23,198 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:75, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:23:23.195861, NotificationData:[]), Results:[StatusCode(Good)], DiagnosticInfos:[])

2021-02-07 16:23:45,175 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:75, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:23:45.172315, NotificationData:[]), Results:[], DiagnosticInfos:[])
2021-02-07 16:23:45,175 - asyncua.client.ua_client.UaClient - DEBUG - publish []
2021-02-07 16:23:45,175 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'2\xd2\x82w\xad\x0f\x99\x9a %\xfaj\xb6\xb9\xaf\xa8\xe7\x13\xe6\xec\x15G\xf7G\x15\xbb\x82\x1d\xda\x17\xafh', Timestamp:2021-02-08 00:23:45.175790, RequestHandle:9, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[]))
2021-02-07 16:24:07,185 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:75, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:24:07.182767, NotificationData:[]), Results:[], DiagnosticInfos:[])
```

Test with MaxKeepAliveCount == 0
```
2021-02-07 16:25:40,994 - asyncua.client.ua_client.UaClient - DEBUG - create_subscription
2021-02-07 16:25:40,994 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: CreateSubscriptionRequest(TypeId:i=787, RequestHeader:RequestHeader(AuthenticationToken:b=b'\x18*m\xa6E\xf3?\x9d\x86\xe2\xe9rgI\xa7\x073\xe90\xdb\x82\x82~F\x81\xe8\xb2T\xdb\xb0\xf8\xea', Timestamp:2021-02-08 00:25:40.994336, RequestHandle:4, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:4000, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:CreateSubscriptionParameters(RequestedPublishingInterval:1000, RequestedLifetimeCount:10000, RequestedMaxKeepAliveCount:0, MaxNotificationsPerPublish:10000, PublishingEnabled:True, Priority:0))
2021-02-07 16:25:45,006 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:76, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:25:45.003386, NotificationData:[]), Results:[StatusCode(Good)], DiagnosticInfos:[])
2021-02-07 16:25:45,007 - asyncua.client.ua_client.UaClient - DEBUG - publish []
2021-02-07 16:25:45,007 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'\x18*m\xa6E\xf3?\x9d\x86\xe2\xe9rgI\xa7\x073\xe90\xdb\x82\x82~F\x81\xe8\xb2T\xdb\xb0\xf8\xea', Timestamp:2021-02-08 00:25:45.007090, RequestHandle:8, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[]))

2021-02-07 16:25:42,023 - asyncua.client.ua_client.UaClient - DEBUG - publish [SubscriptionAcknowledgement(SubscriptionId:76, SequenceNumber:1)]
2021-02-07 16:25:42,023 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'\x18*m\xa6E\xf3?\x9d\x86\xe2\xe9rgI\xa7\x073\xe90\xdb\x82\x82~F\x81\xe8\xb2T\xdb\xb0\xf8\xea', Timestamp:2021-02-08 00:25:42.023578, RequestHandle:7, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[SubscriptionAcknowledgement(SubscriptionId:76, SequenceNumber:1)]))

2021-02-07 16:25:45,006 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:76, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:25:45.003386, NotificationData:[]), Results:[StatusCode(Good)], DiagnosticInfos:[])
2021-02-07 16:25:45,007 - asyncua.client.ua_client.UaClient - DEBUG - publish []
2021-02-07 16:25:45,007 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'\x18*m\xa6E\xf3?\x9d\x86\xe2\xe9rgI\xa7\x073\xe90\xdb\x82\x82~F\x81\xe8\xb2T\xdb\xb0\xf8\xea', Timestamp:2021-02-08 00:25:45.007090, RequestHandle:8, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[]))

2021-02-07 16:25:48,016 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:76, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:25:48.013598, NotificationData:[]), Results:[], DiagnosticInfos:[])
2021-02-07 16:25:48,016 - asyncua.client.ua_client.UaClient - DEBUG - publish []
2021-02-07 16:25:48,017 - asyncua.client.ua_client.UASocketProtocol - DEBUG - Sending: PublishRequest(TypeId:i=826, RequestHeader:RequestHeader(AuthenticationToken:b=b'\x18*m\xa6E\xf3?\x9d\x86\xe2\xe9rgI\xa7\x073\xe90\xdb\x82\x82~F\x81\xe8\xb2T\xdb\xb0\xf8\xea', Timestamp:2021-02-08 00:25:48.017009, RequestHandle:9, ReturnDiagnostics:0, AuditEntryId:None, TimeoutHint:0, AdditionalHeader:ExtensionObject(TypeId:i=0, Encoding:0, None bytes)), Parameters:PublishParameters(SubscriptionAcknowledgements:[]))
2021-02-07 16:25:51,016 - asyncua.common.subscription - INFO - Publish callback called with result: PublishResult(SubscriptionId:76, AvailableSequenceNumbers:[], MoreNotifications:False, NotificationMessage:NotificationMessage(SequenceNumber:2, PublishTime:2021-02-08 00:25:51.012809, NotificationData:[]), Results:[], DiagnosticInfos:[])
```