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 Astropy, the property that was previous called `param_dim` is now called `n_models`.  However, I think that's still very distinctly a feature of Astropy, and mostly a convenience for certain use cases with fitting.  I don't see how it would make sense to include in this more generic data model, where I would be wary of placing too much dependence on Astropy features.