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.   
Add comment on why guess is required only for this class (and its subclass). Is this supposed to be an abstract class for smile model caplet strippers?