Reconnect: stop broadcasting HISTPROV to all clients

[Terkwood]

The reconnect flow in the browser currently relies on the HISTPROV event. This is an event which is currently broadcasted to all clients.

Gateway should stop listening for Kafka HISTPROV events and should instead rely on a wrapper event which deals specifically with reconnect requests keyed by session ID.

This will reduce the network data transfer for the client. HISTPROV can be used entirely behind the scenes to power the new Reconnect wrapper event as well as the Sync Reply