* Remove inheritance of Citation from RefBase, using source_handle filed instead (similar to the way Family objects store mother and father handles) (also use the set_ and get_reference_handle functions more consistently)
* Use get_citation_list instead of get_citation_references (more consistent with the way notes are handled)
svn: r18100
* Updated merge Sources
* Implemented undo-redo for citations (revision 18069 had only added citations to the undo-redo list, not acted on that types of element)
* Fixed embedded lists for some of the object type editors that were done in Rev 18069
* Modified EditCitation so the source parameter is optional
* Added svn properties for all /src/Merge/merge*.py modules
* Added support for EditCitation from backreflist.py
svn: r18085
* Modified Event object to include references to Citations
* Implemented database upgrade for Events (upgrade for Media had already been done)
* Enhanced database upgrade to do backlinks
* Modified Media object to remove sourceref
* Implemented citations bottombar gramplet
* Some minor fixes and improvements
svn: r18054
