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/control/logdisplay.py

@@ -197,6 +197,8 @@ def pretixcontrol_logentry_display(sender: Event, logentry: LogEntry, **kwargs):
         'pretix.user.settings.notifications.enabled': _('Notifications have been enabled.'),
         'pretix.user.settings.notifications.disabled': _('Notifications have been disabled.'),
         'pretix.user.settings.notifications.changed': _('Your notification settings have been changed.'),
+        'pretix.user.oauth.authorized': _('The application "{application_name}" has been authorized to access your '
+                                          'account.'),
         'pretix.control.auth.user.forgot_password.mail_sent': _('Password reset mail sent.'),
         'pretix.control.auth.user.forgot_password.recovered': _('The password has been reset.'),
         'pretix.voucher.added': _('The voucher has been created.'),