Reduce memory overhead and GC churn

Utilize only 2 sets instead of instantiating a new set on each courseID
iteration - should reduce memory overhead and garbage collector churn.
Revert "Reduce memory overhead and GC churn"

This reverts commit 3734b82aff1572c995c7ab014d190166e8fa8d34.
Merge branch 'master' of https://github.com/mikereinhold/Oakland-Scheduler