Implement OAuth2 provider (#927)

- [x] Application management
  - [x] Link
  - [ ] Tests
- [x] Authorize flow
  - [x] Tests
- [x] Refresh token handling
  - [x] Tests
- [x] Revocation endpoint
  - [x] Tests
  - [x] Mitigate: https://github.com/jazzband/django-oauth-toolkit/issues/585
- [x] API authenticator / permission driver
  - [x] Test
- [x] Enforce organizer restriction
  - [x] Tests
- [x] Enforce scope restriction
  - [x] Tests
- [x] Show current applications to user
  - [x] Revoke
  - [x] Tests
- [x] Log new authorizations
  - [x] notify user
- [x] Ensure other grant types are not available
- [x] Documentation
- [x] check if revoking access toking, then refreshing gets rid of organizer constraint
- [x] Show logentry foo

src/pretix/base/models/auth.py

@@ -25,13 +25,13 @@ class UserManager(BaseUserManager):
     model documentation to see what's so special about our user model.
     """
 
-    def create_user(self, email: str, password: str=None, **kwargs):
+    def create_user(self, email: str, password: str = None, **kwargs):
         user = self.model(email=email, **kwargs)
         user.set_password(password)
         user.save()
         return user
 
-    def create_superuser(self, email: str, password: str=None):  # NOQA
+    def create_superuser(self, email: str, password: str = None):  # NOQA
         # Not used in the software but required by Django
         if password is None:
             raise Exception("You must provide a password")