New implementation of CicEnvironment:

New implementation of CicEnvironment:
 a) I have splitted out nCicLibrary from nCicEnvironment
 b) Recursion changed: the nCicTypechecker now registers itself to the
    nCicEnvironment. Then it is the nCicEnvironment.get_obj that retrieves
    an object from the library before calling the registered typecheck_obj
 c) The logger is now called every time NCicTypechecker.get_obj is invoked,
    both by the nCicEnvironment and by another module

TODO: implement trustness