FlightGear - Flight Simulator FGAddon

* The overhead light switch is now a two-position switch and activates
the overhead lights.

* Illuminate the non-backlit areas of the cockpit with the overhead
lights: the charts on the copilot's seat, the instrument panel, the
throttle/RPM/mixture levers, coil flap levers, flap lever, etc.

* The left-hand electrical buttons (main battery, magnetos, start
button, etc.) and the instrument and radio light dimmers are no
longer back-lit and no longer controlled by the instrument light;
instead they are dimly lit only by the overhead light. I believe
this to be more realistic but then again I've never been in an
actual Seneca II, let alone at night :)

* Make the NAV1, NAV2, ADF and DME instruments use the radio light
dimmer (which was previously inoperative) and have the same color;
white, since NAV1 and NAV2 are not specific to the Seneca II but are
shared between various aircraft. Most importantly, the knobs are lit,
too, and therefore visible at night even without Ctrl+C.

* allow-toggle-cockpit=true; toggle with 'c'.

* Save the fuel and payload with the aircraft data.

* Models/dme.xml:
- Do not use a SenecaII-specific copy of the ki266 DME instrument; use
the shared one instead.
- Override the lighting to use the property /controls/lighting/radio-norm
instead of .../instruments-norm.

* Instruments-3d/ki266.{xml,ac}: remove.