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
diff --git a/variables.h b/variables.h
index aeb2669..8da69e9 100755
--- a/variables.h
+++ b/variables.h
@@ -149,6 +149,12 @@
 #define TW_IS_SUPER                 "tw_is_super"
 #define TW_AUTO_REFLASHTWRP_VAR     "tw_auto_reflashtwrp"
 
+// Theme versioning
+// version 2 requires theme to handle power button as action togglebacklight
+// version 4 adds listbox support to reboot page
+// version 5 adds File Manager options, nano & Flash Current TWRP
+#define TW_THEME_VERSION 5
+
 // Also used:
 //   tw_boot_is_mountable
 //   tw_system_is_mountable