STYLE: Cleanup ROI widget and representation

Add vtkMRMLDisplayNode::GetBounds() utility method.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22803 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Cleanup ROI widget and representation

This reverts commit r22803 inadvertently pushed.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22804 3bd1e089-480b-0410-8dfb-8563597acbee
STYLE: Add X,O,M and S documentation for VolumeRendering module

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22805 3bd1e089-480b-0410-8dfb-8563597acbee