Changes to make the AltitudeHold module work as an optional module
Changed to make the PathPlanner module work as an optional module.
Corrected values to be returned and added PathPlanner to OPTMODULES for FlyingF3.
Fixed defines for builtins.
PathPlanner: Make this module optional for all platforms

Now the module supports being optional we should make it this
way for all the other targets.  Especially since having the
PathPlanner enabled without the PathFollower means the system
has a critical error and won't arm.
PathPlanner: Initialize ModuleSettings before using it
Sanity Check: Add check for pathplanner modules running

When the flight mode allows PathPlanner mode that ensure both
a planner and follower are running.

fixes #217
Merge branch 'altitudehold_pathplanner_optional' into next

This merges pull request #217