Map View: Update RATE_CHAN2 request rate to 5Hz

- Improves position of craft on map view.
  There are still very occasional jumps but
  that is possibly due to lot of work being
  done on main thread elsewere in the app.
Merge pull request #77 from fightingwalrus/igcs-129-mapview-position-lag

Map View: Update RATE_CHAN2 request rate to 5Hz