Tracking the entry that is being edited should live on the Model and not Entry

[mrozbarry]

It looks like all the base are covered, but it is theoretically possible for two entries to be marked as editing = True.

Having something like editingEntryId : Maybe String would eliminate that possibility, and be more explicit. It does mean passing around more information into the entry views, though. I also don't know if this is technically any more correct.