Come up with a way to track Snap notifications

[Montoya]

Currently there are no events for notifications. This ticket is to determine what can be tracked and how:

• snap_notify event (with snap_id)
• user views the notifications list
• user marks a notification as read (with snap_id)
• user marks all notifications as read

[Montoya]

I am going to defer this to the Notifications team. Will discuss with Helen.