FlightGear - Flight Simulator FGAddon

More features from Andreas Zenner, slightly modified by myself.

* gui/dialogs/configuration_dialog.xml: new. Allow showing or hiding
the gunsight, magnetic compass, heat tube and stick. Also allow
adjusting the exponent for rudder control.
* MiG-15bis-set.xml: Use it; replace Beginner Mode and Pilot mode
menu items with a single checkbox in the dialog: "Realistic aircraft
failures". Update help text. Add properties for selectable items in
the cockpit.
* Models/Instruments/Headsight/MiG-15bis-Headsight.xml,
Models/Instruments/Magcompass/MiG-15bis-Magcompass.xml,
Models/Instruments/Stick/MiG-15bis-Stick.xml: make optional, using
the properties set forth above.
* Nasal/MiG-15bis.nas: modify failures as follows:
- the gear will not break due to G-forces in flight anymore.
- the gear will break on touchdown depending on vertical speed and
aircraft weight, not horizontal speed alone.
- flaps will tear at 380 and 500 km/h (20 and 55 degrees) instead
of 350 and 450 km/h (with linear interpolation in between, while
the flaps extend or retract).
- drop tanks are now selectable from the configuration dialog and
not just when their contents changes in the fuel and payload
dialog.
- the aircraft disintegrates above 12g instead of 8g (as per
published documentation).
- show vertical speed of each wheel on touchdown (if selected in
the configuration dialog).