Make AssignmentUpdater more concurrency-friendly
Make AssignmentUpdater more concurrency-friendly

There's no reason to do all that in a transaction, and find_each will head off scaling problems.

sejalkhatri/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,sejalkhatri/WikiEduDashboard,WikiEducationFoundation/WikiEduDashboard,sejalkhatri/WikiEduDashboard,sejalkhatri/WikiEduDashboard,sejalkhatri/WikiEduDashboard