Migrate alerter to "User Notifications" framework about taqo-paco

[rundong08]

Some other tips:

1. Notification timeout cannot be managed by the notification center, one have to manage it on their own: keeping the time and asking the notification center to remove the notification at timeout.
2. For a simple notification without action buttons, there are two builtin actions, identified with UNNotificationDefaultActionIdentifier, UNNotificationDismissActionIdentifier. The UNNotificationDefaultActionIdentifier will be sent when you click the notification. The UNNotificationDismissActionIdentifier is supposed to be sent when you dismiss (e.g. close) the notification. However, it will only be sent when one the notification belongs to a category with UNNotificationCategoryOptionCustomDismissAction option enabled.
3. When one removes a delivered notification with removeDeliveredNotificationsWithIdentifiers, the sender app will not know it. One have to do the housekeeping on their own.
4. The completion handler in userNotificationCenter:didReceiveNotificationResponse:withCompletionHandler: method has some async parts. If one exit the app immediately after calling the completion handler, one may get an error complaining the app is already closed and may get an additional empty notification delivered.