TLS 1.3 Support

[shreve]

Not Ready for Review

Things Done:

• Add TLS 1.3 flag support
• Add required TLS 1.3 cipher to list of supported suites
• Update fingerprint to Chrome 72
• Update the process of building TapDance payload to add 1.3 support.

This currently seems to be fulfilling what it needs to do. It's the server that isn't quite ready. (See https://github.com/refraction-networking/tapdance-private/pull/4)

To Do:

• [ ] Clean up extra print statements
• [ ] Update byte shifting mechanism. We agreed to try removing a padding byte from TLS 1.3 connections rather than adding a byte to non-1.3 connections to keep backwards compatibility.
• [ ] Issue a PR to uTLS for the TrafficSecrets() method. This is required, but I want to finalize usage here before bringing in another repo.