Refs #314 -- Read-only REST API (#513)

* initial commit

* API auth

* Hierarchical URLs

* Add session auth

* Strong hierarchy

* Add filters

* Add i18n fields, questions

* More viewsets and serializers

* Ticket download

* Add OrderPosition serializer

* View-level permissions

* More tests

* More tests

* Add basic API docs

* Add REST API to docs frontpage

* Tests for order endpoints

* Add invoice tests

* Voucher and waitinglist tests

* Doc draft

* order docs

* Docs on all viewsets

* Disable DRF docs, style sphinx, style browsable API

* Fix tests

* deprecated imports

* Test foo

* Attendee names

* Fix migration problems

* Remove browsable API, plugin integration

* Doc fixes

src/pretix/control/templates/pretixcontrol/base.html

@@ -232,7 +232,7 @@
                     {% if messages %}
                         {% for message in messages %}
                             <div class="alert {{ message.tags }}">
-                                {{ message }}
+                                {{ message|linebreaksbr }}
                             </div>
                         {% endfor %}
                     {% endif %}