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/presale/templates/pretixpresale/event/index.html

@@ -219,6 +219,13 @@
                     action="{% eventurl request.event "presale:event.cart.add" cart_namespace=cart_namespace %}?next={{ cart_redirect|urlencode }}">
                 {% csrf_token %}
                 <input type="hidden" name="subevent" value="{{ subevent.id|default_if_none:"" }}" />
+                {% if ev.seating_plan_id %}
+                    {% if event.has_subevents %}
+                        {% eventsignal event "pretix.presale.signals.render_seating_plan" request=request subevent=subevent %}
+                    {% else %}
+                        {% eventsignal event "pretix.presale.signals.render_seating_plan" request=request %}
+                    {% endif %}
+                {% endif %}
                 {% include "pretixpresale/event/fragment_product_list.html" %}
                 {% if ev.presale_is_running and display_add_to_cart %}
                     <section class="front-page">