[Enhancement] Turn on and off gold, silver, bronze awards

[jmarquez90]

Background: This doesn't always makes sense when running an event over a period of time.

Taken from UX Improvements for Admins #653. @ismisepaul

[rudosch]

I would find this feature very helpful. Since I use other tools besides SecurityShepherd in training students, I would like to be able to avoid a run on the medals.