ENH: Extend vtkMRMLNodeCallback API adding PrintSelf/GetReceivedEvents

This commit add the GetReceivedEvents and PrintSelf functions.
PrintSelf function displays the list of observed event that have been
invoked. This will be used in tests to display more information in case
the expected event count is different from the actual one.

Issue #3708

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23312 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Add TestClearScene to vtkMRMLNodeTest1

This commit extends the test to check that the event invoked by
either a referencing or referenced node when clearing a scene are the expected
ones.

Issue #3708

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23313 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: Update vtkMRMLNodeTest1::TestClearScene to check ModifiedEvent

This commit extends the test to check for modified event. This will
be useful to update the Node reference system in an attempt to resolve
issue #3708.
BUG: ***WIP*** Possible expected behavior to fix issue #3708