Joystick MAV_AUTOPILOT_GENERIC

[flybrianfly]

Can joystick support be added for MAV_AUTOPILOT_GENERIC? My company produces flight control systems using our own flight software stack and some of our customers would like to use a joystick for pilot input rather than an RC transmitter. Our flight control system reports as MAV_AUTOPILOT_GENERIC. This is possible in Mission Planner, but not QGC. I would expect QGC to send either MANUAL_CONTROL or RC_CHANNELS_OVERRIDE messages. RC_CHANNELS_OVERRIDE could be interesting because we could use the same input plane that we use for RC input and just switch which is used based on whether we see a valid RC_CHANNELS_OVERRIDE message show up.