Prepare for solving https://github.com/kanaka/websockify/issues/71:

Rename self.client to self.request, since this is what standard
SocketServer request handlers are using.
Prepare for fixing https://github.com/kanaka/websockify/issues/71:
Move around functions and methods, so that connection-related and
server-related stuff are close together.

This patch just moves things around - it does not change anything at
all. This can be verified with:

git diff websocket.py | grep ^- | cut -c 2- | sort > removed
git diff websocket.py | grep ^+ | cut -c 2- | sort > added
diff -u removed added
Prepare for fixing https://github.com/kanaka/websockify/issues/71:

* Move traffic_legend.

* Since websocket.WebSocketServer.socket is static, don't call it with
  self.socket.
Try to solve https://github.com/kanaka/websockify/issues/71 by
refactoring. Basically, we are dividing WebSocketServer into two
classes: One request handler following the SocketServer Requesthandler
API, and one optional server engine. The standard Python SocketServer
engine can also be used.

websocketproxy.py has been updated to match the API change. I've also
added a new option --libserver in order to use the Python built in
server instead.

I've done a lot of testing with the new code. This includes: verbose,
daemon, run-once, timeout, idle-timeout, ssl, web, libserver. I've
tested both Python 2 and 3. I've also tested websocket.py in another
external service.

Code details follows:

* The new request handler class is called WebSocketRequestHandler,
  inheriting SimpleHTTPRequestHandler.

* The service engine is called WebSocketServer, just like before.

* do_websocket_handshake: Using send_header() etc, instead of manually
  sending HTTP response.

* A new method called handle_websocket() upgrades the connection to
  WebSocket, if requested. Otherwise, it returns False. A typical
  application use is:

    def do_GET(self):
        if not self.handle_websocket():
	   # handle normal requests

* new_client has been renamed to new_websocket_client, in order to
  have a better name in the SocketServer/HTTPServer request handler
  hierarchy.

* Note that in the request handler, configuration variables must be
  provided by the "server" object, ie self.server.target_host.