ENH: slicer.util: Update getNode methods to optionally use a custom scene

This is particularly useful to retrieve node from a scene different
from the main slicer scene.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23658 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Fix crash in AddArchetypeScalarVolume checking MRMLScene validity

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23659 3bd1e089-480b-0410-8dfb-8563597acbee