Renaming a couple of hooks

Since we're starting with a blank slate, I'm suggesting we rename a couple of hooks

`adapterForType` -> `adapterFor` to mirror `serializerFor` and `modelFor`
`modelTypeFromRoot` -> `typeForRoot` to mirror `pathForRoot`.

I believe these should be hook names should be normalized but I'd love to hear if you think they should be normalized the other direction.

Feedback appreciated.