[Django 1.11] Upgrade to Django 1.11

src/pretix/helpers/debug.py

@@ -1,6 +0,0 @@
-from debug_toolbar.middleware import DebugToolbarMiddleware
-from django.utils.deprecation import MiddlewareMixin
-
-
-class DebugMiddlewareCompatibilityShim(MiddlewareMixin, DebugToolbarMiddleware):
-    pass

src/pretix/settings.py

@@ -258,7 +258,7 @@ try:
     import debug_toolbar  # noqa
     if DEBUG:
         INSTALLED_APPS.append('debug_toolbar.apps.DebugToolbarConfig')
-        MIDDLEWARE.insert(0, 'pretix.helpers.debug.DebugMiddlewareCompatibilityShim')
+        MIDDLEWARE.insert(0, 'debug_toolbar.middleware.DebugToolbarMiddleware')
 except ImportError:
     pass