Fix LUA=NO, remove ModelMixerScriptsPage when support not enabled (#869)

* Trying to align LUA options with radio/src/CMakeLists.txt
-DLUA=NO:  no Lua of any kind
-DLUA=ON:  everything but mixer scripts
-DLUA=YES: also mixer scripts

* Color LCD with -DLUA=NO is probably a rare combination, so it needed a little help with #defines.

* Some strange error using floor function w/o <math> - probably because -DLUA=NO is not normally used w/ color.

radio/src/opentx.cpp

@@ -1499,11 +1499,12 @@ void opentxClose(uint8_t shutdown)
 
   //TODO: In fact we want only to empty the trash (private method)
   MainWindow::instance()->run();
-
+#if defined(LUA)
   luaUnregisterWidgets();
   luaClose(&lsWidgets);
   lsWidgets = 0;
 #endif
+#endif
 
 #if defined(SDCARD)
   sdDone();
@@ -1516,7 +1517,7 @@ void opentxResume()
   TRACE("opentxResume");
 
   sdMount();
-#if defined(COLORLCD)
+#if defined(COLORLCD) && defined(LUA)
   // reload widgets
   luaInitThemesAndWidgets();
 #endif