added slug definition to challenge loader
added slug definition to challenge loader

Crashfreak/maproulette,mvexel/maproulette,mvexel/mr-tnav,osmlab/maproulette,osmlab/maproulette,mvexel/mr-tnav,osmlab/maproulette,Crashfreak/maproulette,mvexel/maproulette,Crashfreak/maproulette,Crashfreak/maproulette,mvexel/maproulette,osmlab/maproulette,mvexel/maproulette