Add sales channels (#1103)

- [x] Data model
- [x] Enforce constraint
- [x] Filter order list
- [x] Set channel on created order
- [x] Products API
- [x] Order API
- [x] Tests
- [x] Filter reports
- [x] Resellers
- [ ] deploy plugins
  - [ ] posbackend
  - [ ] resellers
  - [ ] reports
- [x] Ticketlayouts
- [x] Support in pretixPOS

src/pretix/presale/views/cart.py

@@ -382,7 +382,7 @@ class CartAdd(EventViewMixin, CartActionMixin, AsyncAction, View):
         items = self._items_from_post_data()
         if items:
             return self.do(self.request.event.id, items, cart_id, translation.get_language(),
-                           self.invoice_address.pk, widget_data)
+                           self.invoice_address.pk, widget_data, self.request.sales_channel)
         else:
             if 'ajax' in self.request.GET or 'ajax' in self.request.POST:
                 return JsonResponse({
@@ -405,7 +405,7 @@ class RedeemView(NoSearchIndexViewMixin, EventViewMixin, TemplateView):
 
         # Fetch all items
         items, display_add_to_cart = get_grouped_items(self.request.event, self.subevent,
-                                                       voucher=self.voucher)
+                                                       voucher=self.voucher, channel=self.request.sales_channel)
 
         # Calculate how many options the user still has. If there is only one option, we can
         # check the box right away ;)