Limit the gps location dot update to 1 Hz max

1 Hz is the typical max rate of a GPS, I can see it update more frequently than this, which only conflicts with pan and zoom gestures if done too often.
`ReporterBroadcastReceiver::isUpdateDotScheduled` is updated from one thread in the `updatePositionDotHandler` and is read from a separate thread when the `GPSScanner.ACTION_GPS_UPDATED` intent is received.  Reads and writes need to be done with synchronized getter and setters.