Integrate django-scopes (#1319)

* Install django-scopes

* Fix tests.api

* Update tasks and cronjobs

* Fix remaining tests

* Remove unused import

* Fix tests after rebase

* Disable scopes for get_Events_with_any_permission

* Disable scopes for a management command

src/pretix/control/forms/checkin.py

@@ -1,6 +1,9 @@
 from django import forms
 from django.urls import reverse
 from django.utils.translation import pgettext_lazy
+from django_scopes.forms import (
+    SafeModelChoiceField, SafeModelMultipleChoiceField,
+)
 
 from pretix.base.models.checkin import CheckinList
 from pretix.control.forms.widgets import Select2
@@ -44,3 +47,7 @@ class CheckinListForm(forms.ModelForm):
                 'data-inverse-dependency': '<[name$=all_products]'
             }),
         }
+        field_classes = {
+            'limit_products': SafeModelMultipleChoiceField,
+            'subevent': SafeModelChoiceField,
+        }