* implement new Utils get_source_and_citation_referents
* Update sourceview.py and citationtreeview.py to use it
* Fix editsource.py, where deletion of a source object was not properly dealing with all possible citations
* Update mediaobj.py which still had a remnant of a source_list
* fix _HasTextMatchingSubstringOf filter to deal with text in both sources and citations
svn: r18394