Several changes (the beginning of a new era???)

 1. stuff related to transformations (stylesheets and so on)
    moved from gTopLevel to the new library cic_transformations
 2. porting of the stylesheets to old plain ocaml code by Andrea Asperti.
    Also in cic_transformations.

Disclaimer:
 A. the ocaml transformations are still incomplete and under development.
    They are a bit more performant, though. (just a few order of magnitudes)
 B. the cic_transformation library seems a bit of a mess right now.
    Much clean-up needed.