Support SOCKS5 transport

[sanity]

Supporting SOCKS5 as an alternate transport would be useful for people who wish to use VPNs with Locutus.

There is some code to add SOCKS5 support to libp2p, but it is unmaintained and under the GPL which we can't use. Still, it demonstrates that it's possible and not too difficult.

[planetoryd]

1. Application-level socks5 proxying is a poor security practice, generally, because the user is subject to DNS leaks and faulty configuration that lead to anonymity breach.
2. It can be a bonus if implemented properly. Kernel-level routing has better security but that forces locutus to use proxy all the time.

And the user probably shouldn't be mixing normal transports and socks5 transports if he actually wants anonymity, since adversaries may correlate traffic.

There is an easy way of making Locutus anonymous, to run it behind Lokinet/Nym, but you need it support lokinet addresses or you will burden exit nodes. Whether you like it or not, it's a realistic way of achieving anonymity in the near future

[sanity]

SOCKS5 is just an option for people who really want to run over their favorite proxy or VPN, it isn't a practice I would recommend for anonymity.