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.

Advances #124

Close "Check schoolapps requirements.txt and merge relevant dependencies into pyproject.toml" from #134

https://github.com/jazzband/django-constance/pull/359

- Add django-pwa to pyproject.toml
- Add configuration for django-pwa
- Include PWA configuration and favicon support in base.html
- Include serviceworker.js and adapt it for AlekSIS
- Remove old files

Rationale: django-constance is a bit better maintained and has some
features we need, e.g. injecting config into templates through a context
processor. Also, decoupling the settings definitions from import time
allows us to implement lazy access to the config, so we can later access
them in other variables insettings.py directly.