Bug 1021284 - [camera] [flame] spinner appears after every photo capture

I think the best option is to somehow leverage the `busy` event on Camera (if we can). The reason is, there will likely be more cases where we have to show a loading spinner in the future and it would be nice if we didn't have to make direct calls to the `app` object every time we wanted to do that (especially since we're already automatically hiding the spinner when the `ready` event fires, that would be inconsistent).