Update LFUNs.lyx to current format

Update LFUNs.lyx to current format

gen_lfuns.py does now produce the current file format, and and LFUNs.lyx was
re-created with the updated script.
There is one difference if you compare this version of LFUNs.lyx with the old
version updated by lyx2lyx: All occurences of LyX, TeX etc. in the lfun
descriptions are no longer output as logos. I do consider this as a feature,
since the old version did also output the TeX part of BibTeX as a logo, as well
as places where the names were part of some syntax, e.g. lyx::LyXRC::LyXRCTags.