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

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