bnsgeyer and rmackay9 contributed to these changes
make_safe_shut_down waits for spool down before disarming
remove use of attitude_control::set_throttle_out_unstabilized to consolidate logic between multicopters and tradhelis
add follow to FLTMODEx param descriptions
remove follow's set_velocity method
10hz logging of desired velocity in follow mode
follow mode uses pos error P gain
add send-debug-via-mavlink option
don't enter follow if follow lib is disabled
follow debug slowed to 1hz
disable follow on min-features builds