adding support for hosting thanks.html
dropping debreifing support
store if the given hit/ad combo is sandboxed or not
this "deletes" not "expires" ad (see similar syntax on the psiTurk client side)
routes for task "complete", Addresses NYUCCL/psiTurk#58

where browser wouldn't reload AMT page when experiment is served over http://.  now thanks/closepopup.html are hosted on psiturk server.
handling sandbox server-side