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.