Better insight into known addresses

[sisou]

This is specifically relevant to the in-browser web-client.

Currently, users can only observe connected peers from the web-client. There is no way to see all the known addresses, even those not currently connected. The PoW client for Nimiq 1.x has this feature so that we can populate the Wallet network map with known but unconnected peers.

This is a feature request to add a way to query the node's internal address book. Additionally, it would be nice to be notified about changes to it via emitted events (only nice-to-have).