Next step towards a working roundtrip of files generated by LyX:

Next step towards a working roundtrip of files generated by LyX:
Try to recognize modules.
Again, this is needed because the complete LyX preamble is ignored.
It is not possible to recognize a module in all cases, but at least the simple
ones are handled now. As a prerequisite I also had to revive the filling of
known_environments. This has been removed (probably by accident) some time ago.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@37306 a592a061-630c-0410-9148-cb99ea01b6c8