Add ability to disable Model/QuerySet restrictions on use_query

[Archmonger]

Current Situation

Currently, use_query will generate an exception of a Model or QuerySet isn't returned. This makes it incompatible with external ORMs such as SQLAlchemy or encode/orm

Proposed Actions

Create some kind of interface to remove these restrictions. Needs to be able to handle our current stuff as well, so maybe add two args to the hook:

fetch_recursive_classes=[QuerySet]
fetch_classes=[Model]

Argument variable names might need some more thought.