Adds data source to file input page, refactors reform submission, and improves tests

[hdoupe]

This PR does three things:

1. Adds the data source to the file input page using the same approach as the GUI input page
2. Refactors the reform submission to the worker nodes so that the post data is stored in a namedtuple instead of a dictionary. This replaces a combination of dictionaries and tuples with the class-like namedtuple. In my opinion, this enhances the readability of the code. I'm interested in others thoughts on this though.
3. In order to utilize pytest's parameterize functionality in class methods, the class has to inherit from object. Since many methods needed to be tested with both data_source arguments ('PUF' and 'CPS') and there wasn't much benefit from using django.TestCase, I made this change. For now, this only applies to the TaxBrain static model views tests. However, future PR's should propagate this change to the other views test classes.