Infer model from form name.

Hi, Peter! Great work so far. I have a suggestion :smile:

For the simple cases where a model is backed by a form (e.g. a `User` has a `UserForm`) the model can be inferred based on the name of the form.

I've also made the regex strip `Fixture`, which really should be changed to having the form fixtures not having a `Fixture` suffix, but this demonstrates my thinking.