remove unnecessary assert. the length of results might be different from the length of arguments, for example for delete since we are recursive

!! Warning, API-breaking changes!

When closely reading the spec, events are emitted by one node, and refer
to their SourceNode in an attribute — the SourceNode can and often will
be different from the emitting node.

Until now, python-opcua assumed these two to be identical. This commit
tries to straighten this situation.

To that end, we introduce new parameters in the eventgenerator,
Event-class and all children thereof. The EventGenerator will now try to
honor emitting nodes given to it, but still handle and add SourceNodes.
The InternalSubscription finally serializing and emitting the event is
adapted to this new behavior.

See https://github.com/FreeOpcUa/python-opcua/issues/755
This fixes inconsistent Encoding types when performing
y=variant_to_binary(x) -> x2=variant_from_binary(y) on
auto-generated attributes in the standard address space.

Certificate is only used at higher Server level, no need to store in InternalServer

to_binary() was replaced by variant_to_binary as of commit e1067bac

Deleting a node on which any client holds a datachange-notification
subscription, NodeManagementService._delete_node_callbacks fails because
the size of the dictionary it loops over changes. Here, we solve this by
not using the .items() iterator, but making a copy in form of a list
first ….

shoud be of type Int32

This reverts commit b934a49b.

NotificationData is sometimes None. And that causes an exception that breaks
the flow and no SubscriptionAcknowledgement is created and published
to the server.

Added deprecated warning to the implementation of Basic256 and
Basic128Rsa15 security policies.
Removed usage of security policies Basic256 and Basic128Rsa15 from server example
implementation.
Basic256 and Basic128Rsa15 use both the sha-1 algorithm.
This is considererd not secure anymore since OPC UA Spec 1.04.
See:
http://opcfoundation.org/UA-Profile/UA/SecurityPolicy%23Basic128Rsa15
http://opcfoundation.org/UA-Profile/UA/SecurityPolicy%23Basic256

For details on Basic256Sha256 security policy have a look here:
http://opcfoundation.org/UA-Profile/UA/SecurityPolicy%23Basic256Sha256

All other places use UInt32 for NodeClass. Make sure this is consistent.

Before it only deleted the first level of nodes below the specified
list, which was not what the parameter `recursive` conveyed to the user.