The url is based off of the DOI. Because the DOI is always the same,
making more than one factory instance crashes the detail page.

UnpublishedVettedCommentaryFactory does not have this problem,
as it has an empty DOI field and a valid (random) arxiv identifier.

Basic tests to check response contains commentaires.

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

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.