Add schemas for some astropy.modeling models

As I am reading through this and trying out pyasdf I tried creating schemas for `astropy.modeling` models commonly used for WCS transformations. So here they are.

I think only models which don't define an analytical inverse need the `inverse` definition in the schema so only the polynomials have it here. If this is acceptable I'll add the rest of the polynomials.
You can see examples of examples here:

https://github.com/spacetelescope/asdf-standard/blob/master/schemas/stsci.edu/asdf/0.1.0/core/ndarray.yaml