Upgrade to Django 2.1 (#710)

* Upgrade to Django 2.0

* more models

* i18n foo

* Update setup.py

* Fix Sentry exception PRETIXEU-JC

* Enforce slug uniqueness

* Import sorting

* Upgrade to Django 2.1

* Travis config

* Try to fix PostgreSQL failure

* Smaller test matrix

* staticfiles→static

* Include request in all authenticate() calls

src/pretix/base/models/event.py

@@ -265,6 +265,7 @@ class Event(EventMixin, LoggedModel):
         verbose_name = _("Event")
         verbose_name_plural = _("Events")
         ordering = ("date_from", "name")
+        unique_together = (('organizer', 'slug'),)
 
     def __str__(self):
         return str(self.name)