Fixed import structure because testing was broken

src/pretix/__init__.py

@@ -1,6 +1 @@
 __version__ = "0.0.0"
-
-try:
-    from .celery import app as celery_app
-except ImportError:
-    pass

src/pretix/base/__init__.py

@@ -9,4 +9,9 @@ class PretixBaseConfig(AppConfig):
         from . import exporter  # NOQA
         from . import payment  # NOQA
 
+        try:
+            from .celery import app as celery_app  # NOQA
+        except ImportError:
+            pass
+
 default_app_config = 'pretix.base.PretixBaseConfig'

src/pretix/base/services/mail.py

@@ -72,10 +72,7 @@ def mail(user: User, subject: str, template: str, context: dict=None, event: Eve
 
 
 def mail_send(to, subject, body, sender):
-    email = EmailMessage(
+    email = EmailMessage(subject, body, sender, to=to)
-        subject, body, sender,
-        to=to
-    )
 
     try:
         email.send(fail_silently=False)