Add DataType, Property, and Model support

This is an alternative pull request to #1. The approach taken was not to complicate the api with typing.  It is therefore possible to generate technically invalid Swagger.

A couple of methods were moved to where they belong based on the 1.2 types and the Operation.ResponseClass accessors were removed since they are obsoleted by the inherited Type/Ref accessors.

I've also included some utility methods which I am using to map Java types to Swagger Types & Swagger Formats.