WIP: Add test to assert state of submission changes

When a user closes an exercise for a submission that needs input check that the
submissions state is changed to done.
OK, that's a red herring. The short answer is: not what you think.

A more relevant thing is that this is a controller test, and as such it needs to call the controller.

Look at the tests around line 172. They all make a call `post "/submissions/#{submission.key}/done"` that is what makes the app go. This test needs to call the same endpoint (`post "/submissions/#{s1.key}/done"`) instead of calling `close!` on the exercise.