https://github.com/Bouke/django-two-factor-auth/issues/335#issuecomment-584180803

Use git version of django-material for this

Setting `ALEKSIS_CELERY__EMAIL=true` on environment, or using the
equivalent in a config file, make all user mail sent by Django
asynchronous automatically without needing code changes. At the time of
writing, toggling this setting will e.g. make the notification sender
return immediately, and hand off the actual mail sending to Celery.

This reverts commit cae5ca3d.