BUG: Fix update issues in subject hierarchy when module active

Subject hierarchy tree was not properly updated when reparenting programatically or importing/restoring scene when module was active. This has been fixed and some unnecessary code removed.
More testing added to SubjectHierarchyGenericSelfTest.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23527 3bd1e089-480b-0410-8dfb-8563597acbee