Overlay button is skipping GAUGES if no gauges are configured to be available.
The same happens for overlay customkeys.
Note that GA mode always has an overlay available, the compass.
	modified:   MapWindow_Utils.cpp
	modified:   ../ExpandMacros.cpp
	modified:   ../Multimap.cpp
For CAR TREKKING mode the arrival altitude is always the difference between our altitude and waypoint altitude.
No gliding there!
	modified:   WaypointArrivalAltitude.cpp
(CC) remove obsoleted DEFAULT in _System. It should be updated manually by the time being.