Implement quiescence checker for state transitions

[owickstrom]

Add a "quiescence checker" that debounces ongoing network request events and DOM update events, triggering a new state once settled (as opposed to fixed timeouts after actions), with some max timeout to avoid getting stuck. This should make testing faster because no fixed timeouts are needed.

[owickstrom]

Started looking at this. A quick hack suggests there's a lot to be won in terms of speed.