consequent restructuring:
* introduce separate CitationBaseModel module which encapsulates access to both citation and source fields for the views
* introduce separate CitationListModel and CitationTreeModel modules
* move configuration data from libcitationview to citationtreeview and citationlistview, because the two different views have different data
svn: r18110
* 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