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/control/views/main.py

@@ -1,5 +1,4 @@
 from django.conf import settings
-from django.core.urlresolvers import reverse
 from django.db import transaction
 from django.db.models import (
     F, IntegerField, Max, Min, OuterRef, Prefetch, Subquery, Sum,
@@ -7,6 +6,7 @@ from django.db.models import (
 from django.db.models.functions import Coalesce, Greatest
 from django.http import JsonResponse
 from django.shortcuts import redirect
+from django.urls import reverse
 from django.utils.crypto import get_random_string
 from django.utils.functional import cached_property
 from django.utils.translation import ugettext, ugettext_lazy as _