Add support for reserved seating (#1228)

* Initial work on seating

* Add seat guids

* Add product_list_top

* CartAdd: Ignore item when a seat is passed

* Cart display

* product_list_top → render_seating_plan

* Render seating plan in voucher redemption

* Fix failing tests

* Add tests for extending cart positions with seats

* Add subevent_forms to docs

* Update schema, migrations

* Dealing with expired orders

* steps to order change

* Change order positions

* Allow to add seats

* tests for ocm

* Fix things after rebase

* Seating plans API

* Add more tests for cart behaviour

* Widget support

* Adjust widget tests

* Re-enable CSP

* Update schema

* Api: position.seat

* Add guid to word list

* API: (sub)event.seating_plan

* Vali fixes

* Fix api

* Fix reference in test

* Fix test for real

src/pretix/control/urls.py

@@ -140,6 +140,7 @@ urlpatterns = [
         url(r'^pdf/editor/(?P<filename>[^/]+).pdf$', pdf.PdfView.as_view(), name='pdf.background'),
         url(r'^subevents/$', subevents.SubEventList.as_view(), name='event.subevents'),
         url(r'^subevents/select2$', typeahead.subevent_select2, name='event.subevents.select2'),
+        url(r'^seats/select2$', typeahead.seat_select2, name='event.seats.select2'),
         url(r'^subevents/(?P<subevent>\d+)/$', subevents.SubEventUpdate.as_view(), name='event.subevent'),
         url(r'^subevents/(?P<subevent>\d+)/delete$', subevents.SubEventDelete.as_view(),
             name='event.subevent.delete'),