Managed TCP streams

[OlofBlomqvist]

Rewriting the proxy feature so that we always terminate tls but do not need to terminate http in most cases.
this should dramatically improve performance for cases where tcp tunnel mode is not used.

This pr also adds the ground work for allowing us to capture statistics of in-progress http sessions so that it can be exposed to the web-ui for real-time monitoring of active requests (as in, view normal req/res, websocket messages, http2 streams and so on)

TODO

• Perf: should stay around 170-200k rps for caddy example
• LE still working for all types of sites
• Make sure statistics page works with new mode
• Support tcp tunnel, tls-termination-only (fancy-mode), and tls+http termination (terminating proxy mode)
• Connections page should display the three modes
• Distinguish between the old (unmanaged) tcp tunnel mode and this mode - naming?
• Error handling - no unwraps etc.
• Handle all todo's in the changed code