Implement a cache for BibTeX data. There was a cache of sorts already in InsetCitatio...

Implement a cache for BibTeX data. There was a cache of sorts already in InsetCitation, but that was being used only to cache the labels. So that has been moved to Buffer, and everything else that needs access to BibTeX data should call either Buffer::localBibInfo(), which gives you the BiblioInfo for this Buffer, or Buffer::masterBibInfo(), which gives you the BiblioInfo for the Buffer's master, if it has one, or for it, otherwise. Normally, what you want is masterBibInfo().

Thanks to Andre for help with linking problems.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@24505 a592a061-630c-0410-9148-cb99ea01b6c8