Recording a program should disable on-screen debug controls

There's a button to record programs in CodeWorld. There is also a on-hover feature to add controls for pause, zoom, pan, etc. Unfortunately, the latter debug controls get in the way of recording the video, and appear in the recording.

When a user has clicked Record or (after #848) taking a snapshot, the debug controls should be automatically disabled. This means the Haskell code needs to listen for some kind of signal from the environment to disable that behavior.