Cleaned up CSP.hs and ConstraintGraph.hs. Added Data.Eq.

* mkCG was moved from CSP to ConstraintGraph
* A list of exported functions was added to ConstraintGraph.
* Data.Eq was added, containing the function equating.
* The import of Wolf.hs was removed from Main.hs, since it no longer
works due to the removal of SimpleCSP.hs