Ports changes to models and model tests along with some settings changes...

... from feature/tracks_activation
We do want the MultipleObjectsReturned to be propogated up, since that's not an error we usually want to handle (the intent of this method is to select for things that should be unique, such as an item by primary index).  get_or_404 may be more appropriate with the new error handling changes, so we'll probably replace this with that pretty soon.