Network notifiee callbacks

Nobody has claimed this yet.

I'm thinking if it makes sense to let the daemon register a network notifiee which has both `Connected` and `Disconnected` exposed to the clients in some way(e.g. through the socket which the client is listening). It will allow the clients to be called back right after connected and disconnected events. This is not necessary because we can do it through polling with `list_peers`.

The advantage I can think of now is we can perform handshaking or blacklist checking right after connecting, and be updated when peers have disconnected. The drawback is that it incurs additional complexity to do the callbacks in both the daemon and client.

Start by reading how the daemon communicates with clients through the socket and how list_peers currently exposes network state. Determine where Connected and Disconnected events are available and how callbacks could be represented for clients. Done would require an agreed design and implementation for both event delivery paths, including handshaking or blacklist checks after connection.

Written by the indexing model from the issue text.