Add gates (groups of check-in devices) (#1825)

src/pretix/base/services/checkin.py

@@ -230,6 +230,7 @@ def perform_checkin(op: OrderPosition, clist: CheckinList, given_answers: dict,
             list=clist,
             datetime=dt,
             device=device,
+            gate=device.gate if device else None,
             nonce=nonce,
             forced=force and not entry_allowed,
         )