Airborne home tracker for directional antennas (extending range/saving power/minimize RF impact)

Antenna tracker already exists for the GroundControlStation.
Having two servos pointing directional(s) antenna(s) from plane towards GCS/HomeWP would further extend the range (or optimize the airborne Tx power )

This could be done by adding 2 functions to the channels ouput functions:
1- PAN_TRACK_HOME
2- TILT_TRACK_HOME

Users will then use a 360deg servo controlled by the PAN_TRACK_HOME output
and a 180deg servo controlled by the TILT_TRACK_HOME output
in order to point the aircraft's antennas to Home or GCS (these antennas can then be directional, which will save transmission power and/or extend the range and generate less RF interferences)

PS : in most cases, Home is a fixed waypoint defined when arming. For specific applications, the GCS could be mobile and a telemetry link could be used to use a dynamic home waypoint.

Platforms : Plane, Copter and Rover

Start by locating the existing GroundControlStation antenna tracker and the channel output functions for Plane, Copter, and Rover. Determine how PAN_TRACK_HOME and TILT_TRACK_HOME should use home or a dynamic GCS waypoint, then verify that both servo outputs point the aircraft antennas correctly across the supported platforms.

Written by the indexing model from the issue text.