theme: move TW_THEME_VERSION to variables.h

Automatically add the current theme version to the
splash and ui xmls during the build

Change-Id: I52f8cb41fabe34a8849ecc54ece3c0fb645dcd74

gui/pages.cpp

@@ -53,9 +53,7 @@ extern "C" {
 #include "objects.hpp"
 #include "blanktimer.hpp"
 
-// version 2 requires theme to handle power button as action togglebacklight
-// version 4 adds fastbootd support
-#define TW_THEME_VERSION 4
+#include "../variables.h"
 
 #define TW_THEME_VER_ERR -2