Unregister player (in classroom module) interval and timeout on refresh

[Gloorf]

Currently with the classroom module, events registered by an user are unregistered on reload, which is a really, really, really useful feature (as you don't need to do it yourself or refresh() if you forgot to do it yourself). Unfortunately, this doesn't apply for interval and timeout, resulting in many many refresh() to remove those old interval.

This let the classroom module unregister player-defined interval and timeout, in the same way events handlers are unregistered.