removes get_or_none, 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 accordingly
Merge branch 'develop' into feature/get_or_404_refactor
Merge pull request #40 from penzance/feature/get_or_404_refactor

removes get_or_none