Added an inversion checkbox for each joystick axis so they can be individually inverted or not. This will be a joystick-specific configuration and independent of the autopilot used. Also refactored the code so that the JoystickAxis objects connect directly to the JoystickInput thread for updating the backend. The JoystickWidget is now just a facilitator and doesn't do any redirecting itself.

The hat readings from the joystick now works correctly. Also moved some signals over to using an enum from an int type.

Moved the JOYSTICK_*_MAPPING enum into JoystickInput where it belongs. Also renamed some local variables.

Refactored much of the joystick interface with the largest changes being the removal of dead/unused code including broken event-based SDL reading code. Additionally the mapping code should now work, though it hasn't been tested with controller switching or a real UAS. Finally the existing settings code has been commented-out as it is not compatible with the current state of this code and needs to be able to support different joysticks based on name.

The joystick settings window has now been reworked to be a fixed minimum size and dynamically scale with both the number of buttons and axes on a given joystick/controller. Mapping functionality is incomplete at this point still, though the UI exists for it.