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.
In that case, coeffs could be a dictionary.  But if the keys are just `c0`, `c1`, `c2` etc., I don't see why it couldn't just be a list of numbers, or list of list of numbers...