BUG: 3388. Added observer events parameter to the vtkMRMLNode::AddNodeReferenceRole() method, so that the events can be set only once in subclasses. Added observed events to DisplayableNode and TransformableNode. Simplified and unified reference implementation in TransformableNode

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22523 3bd1e089-480b-0410-8dfb-8563597acbee