Make some methods in FARWingAerodynamicModel overridable

[giuliodondi]

I made a personal fork of the repository and made a couple changes to FARWingAerodynamicModel so that a few methods could be overridden by a custom plugin.

The rationale for this was to create custom aerodynamic models by directly affecting Cl, Cd and moments calculations, which I successfully did with my SpaceShuttleSystem fork.

I'd very much like these changes to be added to the mainline code, there is no business-end change to the functionality, just changes t oa few selected access modifiers.

This way, not only my other mods would be usable without requiring a custom fork, but others could do a similar thing and develop custom aero modules that wuld natively work in FAR

Would you be interested at all?