add yggdrasil service watcher (update every 1s, think about freq)

src/application.vala

@@ -77,7 +77,7 @@ namespace Yggtk {
 			}
 		}
 
-		private void display_current_service_state () {
+		private bool display_current_service_state () {
 			try {
 				if (window != null) {
 					window.set_service_state (yggdrasil_service.get_status ());
@@ -85,6 +85,8 @@ namespace Yggtk {
 			} catch (SpawnError e) {
 				stderr.printf ("Unable to get service state: %s\n", e.message);
 			}
+
+			return true;
 		}
 
         private void update_yggtk () {
@@ -130,6 +132,7 @@ namespace Yggtk {
 				window = new AppWindow (this);
 			}
 			display_current_service_state ();
+			Timeout.add_seconds (1, display_current_service_state);
             window.show ();
         }