AP_NPS: Added library for custom NPS behavior.  (failsafe only for now)
Plane: Integrates AP_NPS_Library.
Plane: Manual override.  Failsafes do not happen in MANUAL mode.
AP_TECS: Add method to get flight stage.
AP_NPS: Improvements to GPS failsafe.
Plane: Improved GPS failsafe handling using AP_NPS class.