STYLE: Add vtkMRMLDisplayableNode method definition to cpp file.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23437 3bd1e089-480b-0410-8dfb-8563597acbee
STYLE: Add vtkMRMLStorableNode method definition to cpp file.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23438 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix "Deleting Unknown Object" warning in mrml node tests

This commits (1) changes the helper node class name associated with the
hierarchy node to be unique and (2) updates the helper node definitions
to be consistent with the helper node declared in vtkMRMLNodeTest1.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23439 3bd1e089-480b-0410-8dfb-8563597acbee