Secure connections with libp2p merged!

[richiejp]

Finally merged secure connections with libp2p. This took longer than most features I have added so far. I guess mainly because I had some misunderstandings about how libp2p worked and because gRPC's API doesn't quite fit with it.

However the end result is really nice, fully encrypted connections using public key cryptography, but the user doesn't need to know anything about how it works. It's on the level of Bluetooth pairing.

One caveat is that to activate it you have to set the host to a p2p multiaddress. The UI/UX here needs some work I think.

#14

After the above PR I updated the README and made it so that the login command sets the default server host address #16