FlightGear - Flight Simulator FGAddon

Make the cockpit controls for the autopilot use the same properties with the
same values as the generic dialog:
* /autopilot/settings/target-vert-speed-fpm becomes /autopilot/settings/vertical-speed-fpm;
* /autopilot/locks/heading=gps-hold becomes true-heading-hold;

In addition:
* /autopilot/settings/nav-arm (never really used) disappears.
* /autopilot/settings/gps-arm (not used by the generic dialog) becomes gps1-arm for
consistency with /autopilot/locks/altitude=gs1-hold.