disable unused HITs in database should check whether HITs are assigned on MTurk

[alicexigao]

Right now, the "disable unused HITs" in database may disable a HIT on MTurk that has been accepted by a worker, and this was causing an issue when a worker submits a disabled HIT and I had to pay their bonus manually. I think the safest way to do this is to check all unused HITs in database and only disable those HITs that are not accepted by a worker on MTurk.

Basically, for clean up during an experiment (maybe possibly after the experiment), I believe these two buttons are useful:

Disable Unassigned HITs on MTurk (Already implemented on Experiment tab): Find all unassigned HITs on MTurk, and check the DB to see if any HIT is in Experiment or Completed state. Only disable the HITs that have not been in an experiment.

Disable Unused HITs in DB: Find all unused HITs in DB, and check whether the HITs are assigned on MTurk. Only delete records of these HITs in DB if they are not assigned on MTurk.