HUGE COMMIT:

HUGE COMMIT:

1) sequent2pres merged into content2pres
2) more functions to render sequents/context/substs to content and then to
   presentation
3) new virtual class NCic.status with methods implementing pretty-printing
   functions (same interface that used to be given in NCicPp); objects of this
   class are now used REALLY ALL OVER the matita code (well, almost...)
4) NCicPp implements a concrete version of NCic.status
   (low level pretty-printer)
5) ApplyTransformation implements a concrete version of NCic.status
   (high level pretty-printer that uses notation). It also exports the boolean
   reference to deactivate the high level pretty printer in favour of the
   low level one
6) some code simplifications here and there (in particular for tactics)
7) return type of BoxPp changed to yield informations about hyperlinks;
   the information is not used yet by the interface and it is not computed
   yet (not that easy to do...)
8) other minor stuff here and there