pb-notify shows a notification when a push is dismissed

[tsani]

Dismissing a push presumably deletes it, which counts as a modification. Hence, an event is send down the eventstream and is picked up by pb-notify. pb-notify does not check whether the push is active before displaying the notification.

Ideally, pb-notify would see that the push has been deleted and remove it from libnotify. This would require keeping track of a map from pushbullet ids to libnotify ids.