Removed ChainedHashTable and MonomialHashTable since they were not used any more, except by a single unit test.
Removed PairTriangle as it is no longer used (it's replaced by the mathic version). Also tiny amount of clean-up.
Moved several classes closer to using MonoMonoid.
Moving S-pair handling to using MonoMonoid.
Starting cleanup of interface of SigPolyBasis.hpp
Moved interface of SigPolyBasis to using MonoMonoid.
Moved the implementation of SigPolyBasis to use MonoMonoid.