[Companion] Show custom control names throughout the UI (& internal refactoring) (#4693)

* [Companion] Introduce new Boards class to further consolidate hardware metadata and remove some globals.

* [Companion] * RawSource::toString() and RawSwitch::toString() can now return custom hardware names (if given a GeneralSettings object) for the following types (respectively):
    SOURCE_TYPE_STICK, SOURCE_TYPE_SWITCH, SWITCH_TYPE_SWITCH, & SWITCH_TYPE_MULTIPOS_POT;
* RawSource::isPot() and isSlider() can now return their own index position in potConfig[]/sliderConfig[];
* Switch indicator strings can be localized if necessary.

* [Companion] Refactor model printers to use new RawSource/RawSwitch capabilities; Simplify model-to-printer mapping scheme in multimodelprinter; Use const ModelData pointer.

* [Companion] Refactor how RawSource and RawSwitch selection combo boxes are populated, using cache-able data models instead of direct manipulation; Refactor some other Helpers function into their own namespace.

* Cosmetics & forgotten qualifier.

companion/src/modelslist.cpp

@@ -247,7 +247,7 @@ void TreeModel::refresh()
   Board::Type board = eepromInterface->getBoard();
 
   if (!IS_SKY9X(board) && !IS_HORUS(board)) {
-    availableEEpromSize = getEEpromSize(board) - 64; // let's consider fat
+    availableEEpromSize = Boards::getEEpromSize(board) - 64; // let's consider fat
     availableEEpromSize -= 16 * ((eepromInterface->getSize(radioData->generalSettings) + 14) / 15);
   }