Cleanup swap stuff, make more robust

While we're discussing the merits or otherwise of !208 (closed), here is some fixes to the swap workflow cherry-picked (and cleaned up) from that branch.

Although not directly reproducible, I'm confident this should fix #556 (closed) and #557 (closed).

The original assumption was that we can start the wifi local repo server, then tell the user it is connected while JmDNS is starting. The plan was for it to be very snappy, so the user could continue using the UI while bonjour was doing its stuff. However, in realtity this results in the possibility of turning swap on and off again while bonjour is still getting ready.

This now makes the user wait both when starting swap, and also when stopping swap. It will provide proper feedback to the user, do it on a background thread (properly) and update the UI when done.

Added some other misc cleanups while there.