Topic/plat 6640 part2

This is the bulk of the new caplet stripping code. The idea is to have a system that makes it easy to add new models. Only a few models are implemented here. Note, some tests are marked as TestGroup.UNIT_SLOW, which will reduce the test coverage on systems that do not run these tests.   
> There is a CapletStripper interface

Yes there is, and it has several implementations. There is no `CapletStripping` interface though.

> CapletStrippingImp (as in implementation) does all the 'work' and can be used directly. The classes that implement CapletStripper encapsulate a particular model, have a higher level API and wrap CapletStrippingImp

This is all true, but it is still confusing that something that isn't an implementation of an interface is being referred to as an "implementation". I suggested `CapletStrippingCore` because it is wrapped by each of the caplet stripper implementations.