Add a new layout syntax CiteEngine to define the citation commands
available for a given citation engine.
Also extend the CiteFormat syntax to allow more customization. This
mechanism, previously used to produce bibliography entries in the
citation GUI based on the BibTeX entrytype, is now also used to
produce the textual labels for citation insets in the buffer view.
Thus citation styles are almost completely customizable by modules.
Modules for the basic, jurabib and natbib engines are implemented.
Layout format incremented to 37.
git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@40820 a592a061-630c-0410-9148-cb99ea01b6c8
