SNI support for HTTP server and client

Working with SNI-enabled hosts on the client was discussed [here](https://github.com/ztellman/aleph/issues/317). Right now it's possible only through tricky `pipeline-transform` machinery. Same goes for the server as you need to plug in [`SniHandler`](https://netty.io/4.1/api/io/netty/handler/ssl/SniHandler.html) instance to the pipeline. It would be nice to have both supported just by setting up appropriate configuration options.

Start by reading the linked issue 317 and reviewing the existing pipeline-transform setup for client SNI. Then inspect the server and client configuration entry points around Netty's SniHandler. Done means both sides expose configuration options that enable SNI without requiring users to modify the pipeline directly.

Written by the indexing model from the issue text.