dummyMeterControl is overcomplicated and underdocumented #341
Description
Currently we have a dummy meter control (implemented in dummyMeterControl.ts which is more or less cribbed directly from SwingSet. In incorporates a bunch of detail that's not relevant to our world, making it confusing to read and more confusing to maintain. At the same time, the documentation provided is inadequate to explain why it's there and what it does. Fix all that. (Note, this was originally flagged as a review comment on PR #317, but what we have now is actually adequate to the job while simplifying it poses a small risk of destabilization. Consequently I'm flagging this as its own issue so the stability risks associated with cleaning it up can be isolated.