Fix citation filters so they no longer try to filter citations with a sources filter. Citation filter now allows specification of both source and citation data. When a citation is shown in a search or a filtered citation tree view, the corresponding source is also shown.

git-svn-id: svn+ssh://svn.code.sf.net/p/gramps/code/branches/maintenance/gramps40@23142 4ae1f11a-8b86-4847-b8af-ab372f36d1fd