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

doc/development/api/customview.rst

@@ -64,7 +64,7 @@ Similarly, there is ``organizer_permission_required`` and ``OrganizerPermissionR
 event-related views, there is also a signal that allows you to add the view to the event navigation like this::
 
 
-    from django.core.urlresolvers import resolve, reverse
+    from django.urls import resolve, reverse
     from django.dispatch import receiver
     from django.utils.translation import ugettext_lazy as _
     from pretix.control.signals import nav_event

doc/development/setup.rst

@@ -18,7 +18,7 @@ External Dependencies
 ---------------------
 Your should install the following on your system:
 
-* Python 3.4 or newer
+* Python 3.5 or newer
 * ``pip`` for Python 3 (Debian package: ``python3-pip``)
 * ``python-dev`` for Python 3 (Debian package: ``python3-dev``)
 * ``libffi`` (Debian package: ``libffi-dev``)
@@ -54,10 +54,6 @@ The first thing you need are all the main application's dependencies::
     cd src/
     pip3 install -r requirements.txt -r requirements/dev.txt
 
-If you are working with Python 3.4, you will also need (you can skip this for Python 3.5+)::
-
-    pip3 install -r requirements/py34.txt
-
 Next, you need to copy the SCSS files from the source folder to the STATIC_ROOT directory::
 
     python manage.py collectstatic --noinput