PathFollowerSettings: add endpoint radius for ground and vtol

This will be used as the radius within which the UAV must come of a waypoint
to be considered to have hit it.
PathFollowers: check if we hit waypoint in endpoint mode

We had left this check out, which didn't matter for PH/RTH modes
but does for using an endpoint target with the pathplanner.
Merge pull request #487 from peabody124/path_endpoint

Path endpoint termination
Merge remote-tracking branch 'taulabs/next' into sc/vrbrain