More Mac integration works - now it is able to load and use GTK+

themes. Configuration interface on ToDo.

This also indicates that URTrator is now able to perform basic
window theming.

ui/mainwindow.go

@@ -29,6 +29,8 @@ type MainWindow struct {
     // Gamemodes.
     gamemodes map[string]string
 
+    text string
+
     // Widgets.
     // The window itself.
     window *gtk.Window