Add statistics endpoint

[OlofBlomqvist]

It would be nice to have statistics and live session information available thru the administration API such that one could create a user interface for exploring this data. One suggested use-case here would be to have a websocket stream all handled requests+replies so that one can explore the requests thru a web interface.

As odd-box uses self-signed certificates for the terminating proxy it would be fairly simple to provide the raw data even when https is used. In the case of direct tunneling where we cannot decrypt the session, we can still provide source+dest addr and other useful information.

edit: should also add uptime info to sites and the whole process