TabletControl: use the path follower FMS for PH and RTH

This code was written before the more sophisticated path following
code and explicitly tried to set the position and use the path
planning code. Now it behaves like the transmitter and simply sets
the flight mode to PositionHold.
SparkyBGC: needs LoiterCommand included
Merge pull request #1282 from peabody124/tablet_control_ph

TabletControl: use the path follower FMS for PH and RTH