Add canonicalization of CG coefficients
Add canonicalization of CG coefficients

The canonicalization facility could attempt to canonicalize CG
coefficients before further simplification.

Since the base drudge amplitude simplification facility does not yet
have a hook to add customized pre-processing steps, also for performance
reasons, CG simplifications are now moved into a separate function.

tschijnmo/drudge,tschijnmo/drudge,tschijnmo/drudge