Write test for bug from last commit.

New Commentary requests were not completed
 as the `requested_by` field was not properly
 saved.

Test if the `vet_commentary_requests` is responding with
 the right Commentary object.

Passwords generated by factoryboy were directly
 put into the table as a string, unhashed! However,
 if the testclient tried to login, it used all
 auth methods a normal user uses as well. This caused
 the test user to never be able to login with the
 generated password.

Add tests to VetCommentary view, however
 the fixtures for groups remain empty (no permissions)
 causing problems with the ContributorFactory. Need some
 fix first, to have the groups work properly with the
 factories.

Add test to check expected ValueError
on processing form before validation.

Add more VetCommentary tests for the
three different possible valid form actions.

Add valid test for accepted `VetCommentaryForm`.
Further added factory for unvetted Commentary.

These are the templates that had to be
within the last commit.

Emails sent from the vet request commentaries
are contains in templates now in the templates folder.

Logic from vet_commentary_request has been moved
to the VetCommentaryForm form. Further moved some
code to improve DRY.

Method test_form_with_duplicate_*'s second part
 gave a false-positive result as the form_data
 contained neither a DOI nor a Arxiv ID. The
 tests came back positive but actually they were
 not.

Add invalid form test for RequestCommentaryForm.
Tests contain having no Arxiv ID or DOI or trying to
 give an already existing identifier.

Add first form tests using Factory to test RequestCommentaryForm.

Move few constants to a seperate file away from models.
This implies minor edits in other apps relying on
these few constants.

This commit contains the first working view test
for the `request_commentaries` view.

Move form validation and saving of instances
to the form class. From here you are able to instantly
save your validated form to the database. Further
reduces the size of the views.
Form may need error handling on not having
found a Contributor before saving the form instance.

Lost order argument in query for CommentarySearchForm
results in the last commit.

Reduce the amount of logic in the `commentaries` and
`browse` views methods in the `Commentaries` app. Further,
added a return method to the `CommentarySearchForm` to help thin
out code in the view.

Implemented basic modelmanager on Commentary
model. Created `vetted` and `awaiting_vetting` methods
and ipmlemented to few view methods.

Commentary model inherits from TimeStampedModel now. It
also includes migrations related to the inheritance:
 - Add added field on Commentary
 - Alter field last_activity on Commentary