* Add Playground struct and basic support for creating it and retrieving
it
* Add missing functions in pwd mock
* Get playground from request domain and validate it exists. If valid set
it on the newly created session.
* Move playground specific configurations to the playground struct and use
it everytime we need that conf.
* Don't allow to specify a duration bigger that the allowed in the
playground
* 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
