improvements to /api/challenges, and adding active to summary.
improvements to /api/challenges, and adding active to summary.

mvexel/maproulette,Crashfreak/maproulette,Crashfreak/maproulette,Crashfreak/maproulette,mvexel/maproulette,mvexel/maproulette,osmlab/maproulette,osmlab/maproulette,osmlab/maproulette,osmlab/maproulette,Crashfreak/maproulette,mvexel/maproulette