[Simulator] Virtual joystick tweaks. (#4666)

* [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).

radio/src/targets/simu/opentxsimulator.cpp

@@ -134,7 +134,7 @@ void OpenTxSimulator::getTrims(Trims & trims)
 {
   uint8_t phase = getFlightMode();
   trims.extended = hasExtendedTrims();
-  for (uint8_t idx=0; idx<4; idx++) {
+  for (uint8_t idx=0; idx < CPN_MAX_STICKS + CPN_MAX_AUX_TRIMS; idx++) {
     trims.values[idx] = getTrimValue(getTrimFlightMode(phase, idx), idx);
   }