[Twisted-web] Support for websockets.

[Mike Mestnik]

As the name suggests Tor2web is a proxy, it does not need to know
anything about the Websocket protocol, it just needs to know the HTTP
protocol and support it's Websocket aspect identified by the
"connection: upgrade" header.

Here is a patch I wrote that adds this support:
https://pastebin.com/MbHVvwNz

Notice the TODO, this is where changes to the twisted.web.client.Agent
are needed... or to just do the HTTP without this helper library.