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
ENH: Adding the capability to process derived items

DerivedItems is a list of file names attributes on the
loadable with the DICOM instances produced by the plugin,
which will be added to the database after loading
the loadable.

From: Andrey Fedorov <fedorov@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23546 3bd1e089-480b-0410-8dfb-8563597acbee
BUG: Create new indexer for each file

Suggested by Steve Pieper as a way to work around potential issues in CTK

From: Andrey Fedorov <fedorov@bwh.harvard.edu>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23547 3bd1e089-480b-0410-8dfb-8563597acbee