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/forms/item.py

@@ -78,7 +78,7 @@ class QuotaForm(I18nModelForm):
         self.instance = kwargs.get('instance', None)
         self.event = kwargs.get('event')
         items = kwargs.pop('items', None) or self.event.items.prefetch_related('variations')
-        self.original_instance = copy.copy(self.instance) if self.instance else None
+        self.original_instance = copy.deepcopy(self.instance) if self.instance else None
         initial = kwargs.get('initial', {})
         if self.instance and self.instance.pk:
             initial['itemvars'] = [str(i.pk) for i in self.instance.items.all()] + [
@@ -370,6 +370,7 @@ class ItemVariationsFormSet(I18nFormSet):
             auto_id=self.auto_id,
             prefix=self.add_prefix('__prefix__'),
             empty_permitted=True,
+            use_required_attribute=False,
             locales=self.locales,
             event=self.event
         )
@@ -430,6 +431,7 @@ class ItemAddOnsFormSet(I18nFormSet):
             auto_id=self.auto_id,
             prefix=self.add_prefix('__prefix__'),
             empty_permitted=True,
+            use_required_attribute=False,
             locales=self.locales,
             event=self.event
         )