Automatically commit objects created by factories in tests

[grahamalama]

#946 (review)

Since we dbsession.commit() everywhere where factories are used, wouldn't it simpler to do it in the factory function?

This would be nicer. factoryboy has an option to automatically commit objects on creation, though when I tried adding that change to #946, but I saw some errors pop up that made it warrant investigation in a separate issue.