User Prefs: add new flag for app-template options

For experimental options, outside the scope of typical preferences.

While templates are developed we might want to make changes
to behavior which aren't fully compatible with typical work-flows.

Instead of mixing these options in with current preferences
expose separately (we could even force disable them when templates
aren't int use)

release/scripts/startup/bl_ui/space_userpref.py

@@ -313,13 +313,14 @@ class USERPREF_PT_interface(Panel):
         sub.prop(view, "pie_menu_threshold")
         sub.prop(view, "pie_menu_confirm")
         col.separator()
-        col.separator()
-        col.separator()
-
-        col.label(text="Screen:")
-        col.prop(view, "show_layout_ui")
 
         col.prop(view, "show_splash")
+        col.separator()
+
+        col.label(text="App Template:")
+        col.label(text="Options intended for use with app-templates only.")
+        col.prop(view, "show_layout_ui")
+
 
 
 class USERPREF_PT_edit(Panel):