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/waitinglist.py

@@ -77,7 +77,7 @@ class WaitingListEntry(LoggedModel):
         WaitingListEntry.clean_itemvar(self.event, self.item, self.variation)
         WaitingListEntry.clean_subevent(self.event, self.subevent)
 
-    def send_voucher(self, quota_cache=None, user=None, api_token=None):
+    def send_voucher(self, quota_cache=None, user=None, auth=None):
         availability = (
             self.variation.check_quotas(count_waitinglist=False, subevent=self.subevent, _cache=quota_cache)
             if self.variation
@@ -114,8 +114,8 @@ class WaitingListEntry(LoggedModel):
                 'email': self.email,
                 'waitinglistentry': self.pk,
                 'subevent': self.subevent.pk if self.subevent else None,
-            }, user=user, api_token=api_token)
-            self.log_action('pretix.waitinglist.voucher', user=user, api_token=api_token)
+            }, user=user, auth=auth)
+            self.log_action('pretix.waitinglist.voucher', user=user, auth=auth)
             self.voucher = v
             self.save()