put citation dialog in good state:

put citation dialog in good state:
- natbib style (the combox) works
- when moving/up down the item stays selected (allowing sequential ups/downs)
- when deleting the next selected entry gets focus (allowing sequential deletes)
- the info is now shown and updated
- find subsets the available entries as you type
- no additional find dialog (removed QCitationFind.ui)
- selecting with double-click
- removal of unused: Citation class, toVector() function

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@14252 a592a061-630c-0410-9148-cb99ea01b6c8