added new tests and refactored some previous tests
* removed tests that essentially covered form/field rendering
* added more edge-case tests (Proxy models, MTI models, filtering through relationships)
* moved most of the tests which performed queryset filtering to new filtering_tests.py
* added "pragma: nocover" in a few places for coverage.py to omit for reporting
* included fix for generic view error inside of ImproperlyConfigured handler