Due to the new Commentary request forms, which were
also used during vetting (choice=modify), the vetting
went wrong sometimes.
If the vetting action was 'modify', the user was redirected
to the old form which didn't exist anymore.

As a result of how the contruction of this modify structure, the Commentary
was first deleted and thus the data was lost. The requester did receive
a mail that his/her Commentary was accessible on SciPost however.

I fixed this by recontructing the vetting views. I combined the
vetting list and the vet request. I removed the action removing
the Commentary and made this a redirect to a new view which is
a modify page accessible only for EdCol Admins to modify+accept
the Commentary. Also, the mail for 'modify' vetting is also just sent
at *after* modification now.

Add tests for RequestPublishedArticleForm

Write test for bug from last commit.

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.

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.