GCS_MAVLink: generated files for new geofence SYS_STATUS & CMD messages
Plane: now sending MAV_SYS_STATUS_GEOFENCE status.
Plane: Now maintaining previous control mode in a global state variable.
Plane: Fixed bug.  Now goes to previous control mode when leaving GUIDED

    Also laying foundations for automatic and GCS enabled fences:
        Geofence now knows when PWM caused the fence to enable.
Plane: Fence changes to allow for auto and gcs enabled fences.