Support providing objecttype for the method add_object of Node

accept subscription to event type list

Must  be reviewed, do not merge

Implement Subscription Supports List of Event Types, History Update
again after all the changes to events.

fix, renaming and restructure of event stuff

Adding the methods necessary for Modifying Subscriptions, make deadband filters and also added support to deadband filter on server side.

default strings and ByteString to None

small renaming, mv more methods to events.py

implement dict based event history, cleanup event stuff

event history api tweak

take event as arg not evfilter
return EventResult obj and not fields
update command line to read events

Correctly handle count parameter when saving history

WhereClause support

* Added missing handling of the count parameter to the sqlite implementation
* Add tests for both limits and both history implementations
* Fixed some minor issues

The test code is currently setting a limit of 10 history data values.
However, the limit handling is not implemented in both history
implementations and therefore the limit is never enforced.
Removed the limit from the history tests to ensure that no tests are broken
when the limit handling is actually implemented.

The current implementation is actually a no-op since the data is truncated
correctly but not assigned back to self._datachanges.
Pop the first value instead since this function is called for every
datachange which means that not more than one value will every be removed
in a single call.