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/static/pretixpresale/js/ui/main.js

@@ -197,6 +197,11 @@ $(function () {
                     is_enabled = true;
                 }
             });
+            $(".input-seat-selection option").each(function() {
+                if ($(this).val() && $(this).val() !== "" && $(this).prop('selected')) {
+                    is_enabled = true;
+                }
+            });
         }
         if (!is_enabled) {
             $("#btn-add-to-cart").prop("disabled", !is_enabled).popover({'content': gettext("Please enter a quantity for one of the ticket types."), 'placement': 'top', 'trigger': 'hover focus'});
@@ -205,7 +210,8 @@ $(function () {
         }
     };
     update_cart_form();
-    $(".product-row input[type=checkbox], .variations input[type=checkbox], .product-row input[type=radio], .variations input[type=radio], .input-item-count").on("change mouseup keyup", update_cart_form);
+    $(".product-row input[type=checkbox], .variations input[type=checkbox], .product-row input[type=radio], .variations input[type=radio], .input-item-count, .input-seat-selection")
+        .on("change mouseup keyup", update_cart_form);
 
     $(".table-calendar td.has-events").click(function () {
         var $tr = $(this).closest(".table-calendar").find(".selected-day");