* Use Compact when possible, like no signals (see http://live.gnome.org/Vala/ReferenceHandling)
 * Try to replace multiple GObject in App by a data memeber :
    public enum AppType {
        WM,
        PANEL,
        DESKTOP
        }
    public class App {
        private AppType type;
    }
 * Implement stages from GNOME
 * Find a clean solution to the enable flags with automake (see http://lists.gnu.org/archive/html/bug-automake/2013-07/msg00002.html)