ENH: Remove unused Texture and NCI volume rendering mappers

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23026 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Editor updates Volume Rendering when a new label is added

Closes #3076

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23027 3bd1e089-480b-0410-8dfb-8563597acbee