Fully qualified model types (#244)

* Fully qualify types from models

For a long time, we've been fully qualifying depdency types but not model types. This produces code that's fine, but it's always been a confusing inconsistency and it posed problems trying to render Opaque types that specified namespaces (because the namespace was ignored).

This removes that inconsistency.

* A few more small refactorings

* Fix test failures

* CR feedback