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/templates/pretixcontrol/pdf/index.html

@@ -1,6 +1,6 @@
 {% extends "pretixcontrol/event/base.html" %}
 {% load i18n %}
-{% load staticfiles %}
+{% load static %}
 {% load compress %}
 {% block title %}{% trans "PDF Editor" %}{% endblock %}
 {% block custom_header %}

src/pretix/control/templates/pretixcontrol/pdf/webfonts.css

@@ -1,4 +1,4 @@
-{% load staticfiles %}
+{% load static %}
 
 {% for family, styles in fonts.items %}
 {% for style, formats in styles.items %}