Allow nodes to actively request information of a specific peer

For end-to-end encryption and direct connections, the node needs the public key or the endpoints of the recipient. The node should, therefore, be able to request information about a specific peer from the nearest super-peer.

Therefore we should introduce a WhoisMessage, which is sent by the requesting node and contains the address of the requested node. This message is then sent to the respective super-peer, which can look up the address in its local PeersManager. If it has the required information, it sends a PeerInformationMessage to the requesting node. If not, the WhoisMessage is forwarded to the own super-peer.

Each super-peer on the route to the requesting node should read the information contained in the PeersManagerMessage when forwarding and write the information to its local PeersManager.