[rotorcraft] add a HOME mode

Add a HOME mode similar to HOME mode in fixedwing firmware.

Still missing: Getting out of HOME mode via clicking on Navigation Mode indicator in the GCS strip.
This currently only works for fixedwings, because it expects a pprz_mode setting and in [strip.ml] [1] the value is hardcoded to 2 (AUTO2 in fixedwing).

Feedback welcome.

[1]: https://github.com/paparazzi/paparazzi/blob/master/sw/ground_segment/cockpit/strip.ml#L381