Displaying connection and distance/time variants

- Shutting down threads from Closing event. StateWatcher could block
when shutting down from Closed as the window dispatcher was no longer
being processed.
- Fixed distance extra byte to be tenths, not centimetres.
- Exposed ConnectionState to display.
- No longer using RoundedMetres, to be consistent with PM3 display.
- Updating display more often, as looked jittery before.