Notification counts

This PR introduces some improved notification counting functionality. The aggregator will keep track whether a routed activity aggregated with an existing activity. When it does it will not be counted towards the unread count.

This does introduce a breaking change to the format of push notifications. Since we're now publishing on aggregation it's possible to have multiple activities.
Can you also generate a notification of a different type in this test and ensure that that causes the notification count to go up by 1?