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/presale/templates/pretixpresale/event/base.html

@@ -8,6 +8,7 @@
     {% block title %}{% endblock %}{% if url_name != "event.index" %} :: {% endif %}{{ event.name }}
 {% endblock %}
 {% block above %}
+    <script type="text/javascript" src="{% static "pretixpresale/js/ui/iframe.js" %}"></script>
     {% if not event.live %}
         <div class="offline-banner">
             <div class="container">
@@ -24,12 +25,13 @@
     <div class="page-header">
         <div class="pull-left">
             {% if event_logo %}
-                <a href="{% eventurl event "presale:event.index" %}" title="{{ event.name }}">
+                <a href="{% eventurl event "presale:event.index" cart_namespace=cart_namespace|default_if_none:"" %}"
+                        title="{{ event.name }}">
                     <img src="{{ event_logo|thumbnail_url:'logo' }}" alt="{{ event.name }}" class="event-logo" />
                 </a>
             {% else %}
                 <h1>
-                    <a href="{% eventurl event "presale:event.index" %}">{{ event.name }}</a>
+                    <a href="{% eventurl event "presale:event.index" cart_namespace=cart_namespace|default_if_none:"" %}">{{ event.name }}</a>
                     {% if not event.has_subevents %}
                         <small>{{ event.get_date_range_display }}</small>
                     {% endif %}