[Tracking] Implement RLPx transport protocol

[mpaulucci]

https://github.com/ethereum/devp2p/blob/master/rlpx.md

We need this to communicate between nodes on the p2p network

Relevant issues:

• Implement RLPx handshake #125
• Implement RLPx framing #126
• Multiplex between capabilities according to msg-id #171
• Implement RLPx "p2p" capability #127
• Implement missing p2p message handlers #1030
• [Tracking] Implement RLPx "eth" capability #128
• Implement RLPx "snap" capability #184
• Set mechanism to configure node's keys and id #836
• Initiate RLPx connections from discv4 #837
• Build proper RLPx listen loop and peers listen loops #840
• RLPx - Implement Hello messages exchange after Handshake #841
• Fix and add RLPx connection tests #843
• Improve error handling in RLPx modules #845
• Fix bootnode parser #905
• Replace all p2p protocol info! messages by debug! messages #1134
• Add peer information to RLPxConnection struct #1135
• Refactor peer listen-loop to detach socket listening. #1550