AntennaTracker: lots of new parameters

YAW_SLEW_TIME, PITCH_SLEW_TIME, MIN_REVERSE_TIME, START_LATITUDE,
START_LONGITUDE and STARTUP_DELAY

See the parameter docs for explanations
AntennaTracker: added STOP mode

to stop tracker moving
AntennaTracker: fixed ballerina and more accurate tracking

implement new parameter options
AntennaTracker: fixed APM2 serial speed handling

need to change based on USB mux status