Delete notification when they are clicked

lib/ui/screens/notifications_screen.dart

@@ -121,6 +121,8 @@ class _NotificationsScreenState extends State<NotificationsScreen> {
           child: Text(tr("You do not have any notification now.")),
         ),
       );
+
+    throw Error();
   }
 
   /// Delete a notification
@@ -272,8 +274,12 @@ class _NotificationTile extends StatelessWidget {
     } else if (notification.onElemType ==
         n.NotificationElementType.FRIENDSHIP_REQUEST) {
       openUserPage(userID: notification.fromUser, context: context);
+    } else {
+      showSimpleSnack(context,
+          tr("This kind of notification is not supported yet by this application."));
+      return;
     }
 
-    // TODO : mark the notification as seen
+    onDelete(notification);
   }
 }