Refactoring P2P setup code and set up new DB layer framework

[delbonis]

This PR replaces the peer connection code with a new event-based system. It's not complete and there's some things that will be changed in the future. Some changes will be made in a future PR as they're waiting on another thing to happen. A rebase will be needed after the new integration test framework is merged.

TODO:

• [x] Connecting to peers, listening for connections
• [x] Fully persistent peer ids
• [x] Disconnecting
• [ ] DB stuff
  • [x] Storing/loading PeerInfo
  • [ ] Wallet database (outpoints to watch, spendable utxos, etc.)
  • [ ] Channel info
  • [ ] DLC stuff
• [x] Connecting through a proxy
• [x] NAT holepunching, etc.

(Crossed out items are likely postponed until other refactors have been done.)

[gertjaap]

retest this please

[delbonis]

:cold_sweat: those merge conflicts

although many of them I think are just confused imports

[Varunram]

Yeah - wonder why it gets confused on imports / whitespace errors..