Fix #277 -- Embeddable shop (#622)

* Vendor vue.js

* Refactor item_group_by_category to support vouchers

* Widget: Show product list

* Widget: free prices

* Widget: pictures and loading indicator

* Widget: First iframe steps

* Widget: Do not rerender iframe

* Widget: Error handling

* Improve widget

* Widget: localization tech

* Fix invoice style

* Voucher attribute and waiting list

* Add some iframe chrome

* First step to namespaced carts

* More isolation steps

* More cart isolation things

* More cart isolation things

* Mobile stuff

* Show cart on checkout pages

* PayPal and Stripe support

* Enable downloads

* Locale handling

* change text "save URL to this exact page"

* Widget: voucher redemption

* Widget: CSS

* CSS: Responsive

* Widget: CSS improvements

* Widget: Add embedding code generator

* Widget: Error messages and SSL check

* First tests

* Widget: tests

* Don't use IDs in widgets

* Widget: static files caching

src/pretix/plugins/stripe/views.py

@@ -8,9 +8,11 @@ from django.db import transaction
 from django.http import Http404, HttpResponse
 from django.shortcuts import get_object_or_404, redirect
 from django.urls import reverse
+from django.utils.decorators import method_decorator
 from django.utils.functional import cached_property
 from django.utils.translation import ugettext_lazy as _
 from django.views import View
+from django.views.decorators.clickjacking import xframe_options_exempt
 from django.views.decorators.csrf import csrf_exempt
 from django.views.decorators.http import require_POST
 
@@ -193,6 +195,7 @@ class StripeOrderView:
         return self.request.event.get_payment_providers()[self.order.payment_provider]
 
 
+@method_decorator(xframe_options_exempt, 'dispatch')
 class ReturnView(StripeOrderView, View):
     def get(self, request, *args, **kwargs):
         prov = self.pprov