remove user from challenge on logout
proper logout:
+ if logging out user is in challenge, remove him
+ if he is the master of the challenge, pass the status to the next one in the list
+ if he is the last one in the challenge, delete it !
proper logout:
+ if logging out user is in challenge, remove him
+ if he is the master of the challenge, pass the status to the next one in the list
+ if he is the last one in the challenge, delete it !