ENH: Minor subject hierarchy enhancements

If a subject hierarchy node is deleted that has children, the user is given the option to delete branch.
Subject hierarchy added to favorite module list (still not appearing, because QSettings is pre-loaded from somewhere)

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23545 3bd1e089-480b-0410-8dfb-8563597acbee