Use tabs to separate normal and RGB mode

Author: Zorbatron

src/main/java/gregtech/api/mui/GTGuiTextures.java

@@ -643,6 +643,7 @@ private static String id(String path) {
             "textures/gui/progress_bar/progress_bar_fluid_rig_depletion.png", 190, 14);
 
     // MISC
+    public static final UITexture RGB_GRADIENT = fullImage("textures/gui/widget/rgb_gradient.png");
 
     public static void init() {/**/}