This reverts commit ba30cdb6.

Otherwise, use real-time updating (AlekSIS, by contract, is guaranteed
to be slow without Celery ;)).

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

Use git version of django-material for this

https://github.com/silviolleite/django-pwa/issues/34

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.