Set current user when delaying bulk-assignment callbacks
Set current user when delaying bulk-assignment callbacks

Bug report: no e-mail notification when bulk-assigning items. This was happening because `User.current` was not set for the background job that fires the callbacks of a bulk-assignment. The fix is to pass the current user to the background job and set `User.current` from inside the background job.

Fixes CHECK-2048.
meedan/check-api,meedan/check-api,meedan/check-api,meedan/check-api,meedan/check-api