* [Simulator] Create a reusable RadioTrimWidget; Move all trim-related enums to boards.h; Make sure aux trims are accounted for in SimulatorInterface; Trims now use toolbuttons with icons instead of pushbuttons with text.
* [Simulator] New buttons & icons for virtual joystick axis hold/fix toggles; Joystick ball is now slightly scaled to stick area.
* [Simulator] Virtual joystick now "follows" mouse clicks within the stick area (left-click on empty space will attract the control node).
