Added failing test for get_objs_for_user.

This failing test shows that objects under one class can be
returned when get_objs_for_user is called to return objects of
another class due to lacking filtering in get_objs_for_user.
Fixed issue with invalid objects being returned

`get_objs_for_user` was previously not limiting the returned
objects to the specific model, so it would return all objects for
all models specified in the settings when called.  It also wasn't
limiting the scope to the specific permission, so this caused
any expected errors, none of which we had tests to cover.

There were also a few PEP8 fixes included in this.
Added a few more tests

Added some tests which run through a few different combinations
that users may encounter with `get_objs_for_user` and what the
expected results are.
Merge pull request #2 from Rediker-Software/issue_1

Issue 1: Fix filtering in get_objs_for_user