Async

The operation deferral has now been hand-tested.
I think ``serve_api`` and ``serve_networks`` might work well.  I do agree that the name of ``serve`` should change.  (I also think that a different server should do headnode operations---we can't block networking changes on a 20-second headnode cloning process.  For that matter, we can't block 20-second headnode cloning processes on eachother either, so that server has to be structured differently anyways.)