Update Netty dependency to latest, include netty-tcnative-boringssl-static, clean up SocketFactory

Netty 4.1.37 was just released, and among other things, it includes the changes we asked for to allow overriding the queues used for event loops cleanly. Previously we had to resort to reflection to override the undesired behaviour, but now can do it all cleanly.

Additionally, start bundling netty-tcnative-boringssl-static, so that end-users don’t need to do anything extra to take advantage of faster boringssl-based encryption.

And on top of it just generally clean up some stuff in SocketFactory.