Ifc cleanup

[GlenRSmith]

There are currently issues with the three abstract base classes defined in crypt_ifc, and their implementing child classes.
Some places it's the method on the child class that just deviates from a "good" signature on the abc, some places the abstract method signature is too specific to a particular implementation so that other implementations have mismatched signatures.
In general, the abstract methods should be defined with "least common denominator" parameters, always ending with **kwargs, and each implementation has to unpack its specific kwargs for required params. Probably the most disruptive part of the work to tidy this all up will be backtracking the implementations that inappropriately drove the abstract method signatures.