* Refactor to more easily support additional config options
* Notify when Manager.from_queryset happens inside model class body
- A warning will be emitted whenever `Manager.from_queryset` happens
inside of a model class body
* Resolve generated default manager types before final iteration
A default manager on a model should always exist, eventually. Although,
we extend to look through dynamically generated managers on each
iteration instead of deferring until the final iteration.
