Fix #549 -- Multiple PDF ticket layouts (#938)

- [x] Data model
- [x] CRUD
- [x] Editor
- [x] Migration from old settings
- [x] Clone files when copying events
  - [x] badges?
- [x] Actual ticket output
- [x] Default layout on event creation
- [x] Link well from ticketing settings
- [x] Tests
- [x] Shipping plugin
  - [x] Migration
  - [x] Settings
  - [x] Create default
- [x] API

src/pretix/plugins/ticketoutputpdf/api.py

@@ -0,0 +1,31 @@
+from rest_framework import viewsets
+
+from pretix.api.serializers.i18n import I18nAwareModelSerializer
+from pretix.api.serializers.order import CompatibleJSONField
+
+from .models import TicketLayout, TicketLayoutItem
+
+
+class ItemAssignmentSerializer(I18nAwareModelSerializer):
+
+    class Meta:
+        model = TicketLayoutItem
+        fields = ('item',)
+
+
+class TicketLayoutSerializer(I18nAwareModelSerializer):
+    layout = CompatibleJSONField()
+    item_assignments = ItemAssignmentSerializer(many=True)
+
+    class Meta:
+        model = TicketLayout
+        fields = ('id', 'name', 'default', 'layout', 'background', 'item_assignments')
+
+
+class TicketLayoutViewSet(viewsets.ReadOnlyModelViewSet):
+    serializer_class = TicketLayoutSerializer
+    queryset = TicketLayout.objects.none()
+    lookup_field = 'id'
+
+    def get_queryset(self):
+        return self.request.event.ticket_layouts.all()