Fixed Compiler Error C2864 - only static const integral data members can be initialized within a class

Vastly improved the joystick documentation, removed some redundant/unnecessary code, and fixed a couple of small bugs. This code should be ready for live testing.

Have settings loaded/stored correctly for all joysticks based on their UAS type and autopilot type. Switching between UASes doesn't work right yet, however.

The default UAS.cc now lists available actions that it can be commanded. These are polled by the Joystick Configuration window for each joystick button so that they can be assigned to trigger this action. Button presses don't yet trigger these actions, nor are they stored and reloaded on UAS switch.

The joystick code now understands if a UAS can reverse or not (based on UASInterface::systemCanReverse) and scales the joystick input accordingly. This isn't ideal on auto-centering axes and so the limit-range code should be brought back as an option for the throttle channel.

The UASInterface now defines a systemCanReverse() function for indicating if the UAS is capable of commanding a reverse thrust.