Changed the supervisor structure of Chut as a whole
The current way to manage supervision is to have each user of the system living on his own. There is no top supervisor and terminating a given user is done by killing its supervisor.
This new revision adds a new top-level supervisor (chut_user_supersup) which will create and terminate every user process. Adding this supervisor will allow making sure no rogue processes are living and will allow to start and stop chut as a whole with ease.