Addressed the requests in issue #1285

`getfieldInfo` can now also take a source index as argument. Plus it was modified to also handle "telem1+" etc.
New functions `getSourceIndex(sourceName)` and `getSourceName(sourceIndex)` were added, which use the names shown on the
screen instead of the special names table used by `getFieldInfo` and `getValue`.
Indices are the same for all of the functions, so `getValue(sourceIndex)` also works with indices from `getSourceIndex`.
New iterator functions `sources([first[, last]])` and `switches([first[, last]])` for getting ranges of sources and switches.
`getPhysicalSwitches` was removed, as I consider the iterator function to be a better solution.

radio/src/lua/lua_api.h

@@ -208,10 +208,12 @@ extern uint8_t instructionsPercent;
 
 struct LuaField {
   uint16_t id;
+  char name[20];
   char desc[50];
 };
 
 bool luaFindFieldByName(const char * name, LuaField & field, unsigned int flags=0);
+bool luaFindFieldById(int id, LuaField & field, unsigned int flags=0);
 void luaLoadThemes();
 void luaRegisterLibraries(lua_State * L);
 void registerBitmapClass(lua_State * L);