BUG: Add virtual method onMRML{View,Slice}NodeModifiedEvent to vtkMRMLAbstract{ThreeD,Slice}ViewDisplayableManager

These methods could be overloaded by DisplayableManager to re-act upon a modified
event of the associated DisplayableNode (either a MRMLView node or a slicer view node)

That should fix the crash happening after the MRML view node name was updated in the
MRML node inspector of the Data module.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@14577 3bd1e089-480b-0410-8dfb-8563597acbee