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/plugins/ticketoutputpdf/exporters.py

@@ -85,7 +85,13 @@ class AllTicketsPDF(BaseExporter):
             with language(op.order.locale):
                 buffer = BytesIO()
                 p = o._create_canvas(buffer)
-                layout = o.layout_map.get(op.item_id, o.default_layout)
+                layout = o.layout_map.get(
+                    (op.item_id, op.order.sales_channel),
+                    o.layout_map.get(
+                        (op.item_id, 'web'),
+                        o.default_layout
+                    )
+                )
                 o._draw_page(layout, p, op, op.order)
                 p.save()
                 outbuffer = o._render_with_background(layout, buffer)