New implementation of sales channels (#4111)

Co-authored-by: Martin Gross <gross@rami.io>

src/tests/base/test_payment.py

@@ -220,6 +220,7 @@ def test_availability_date_order_relative_subevents(event):
         status=Order.STATUS_PENDING,
         datetime=now(), expires=now() + datetime.timedelta(days=10),
         total=Decimal('46.00'),
+        sales_channel=event.organizer.sales_channels.get(identifier="web"),
     )
     OrderPosition.objects.create(
         order=order, item=ticket, variation=None, subevent=se1,