We can improve the ease-of-use of the Buttons feature (see wiki here) by allowing the user to directly select the function they want attached to the button instead of having to manually look up the number on the wiki page. This should be possible by simply copying the RCx_FUNCTION parameter descriptions @values field to the BTN_FUNC1/2/3/4

There seems to be some issues with the landing function in ./software/px4_mavros_scripts/1_px4_mavros_offboard_controller/commander.py.

To do:

1. Test the land function and report if it works well.
2. Fix if there is an issue.