Add options for separate client/server websocket settings

I'm running Pydio in a container, it's not able to see/access the host machine's IP address.

If I set the IP to the container's IP, the websocket server can start, but the client can't connect.

If I set the IP to the host machine's IP, the websocket server can't start (since it's unable to bind to that address).

This separates the server and client parameters. I believe this will allow admins to setup proxying as well.