removes get_or_none

Removes get_or_none base model classmethod, replacing instances with get_object_or_404, or with try/catch DoesNotExist, as appropriate.

Changes urls of submit_edit pages to take object_id as a url parameter rather than a post parameter.

Updates tests and templates accordingly.
Just curious: is catching the resulting Http404 part of the client.post method, or does it interact with the existing Django middleware that catches exceptions?  I was expecting to see an assertRaises here, but that doesn't seem like it would work with how this is being called.