* Add DNS support for PWD instances
* Store IP address of PWD in all session networks and restore it with the
same IP address
* Remove unnecesary print
* Change url format to pwd<ip>-port for better DNS filtering
* Make PWD listen on 80 and 443 for DNS resolve to work
It works by using the Host of the request. When it receives something in
the form of: `<node>.<session>.play-with-docker.com` it does a reverse
proxy http request to `node`, validating that the `node` actually belongs
to the `session`.
If the node has a prefix `ip` and continues with a valid IP address
where the dots where replaces by underscores (like `ip10_0_0_1`) then it
will remove the `ip` prefix and and replace the underscores by dots, and
assume it is an ip address.
