Send update emails about running appointments

[sander]

It would be nice to give users the option to receive daily updates about running appointments. They could contain information like who has entered their availability, and what new dates were proposed.

I'm not sure yet how to do this. These apps might be useful:

https://github.com/jtauber/django-mailer/ https://github.com/jtauber/django-notification/

Here's a home-grown solution to a comparable problem:

https://github.com/evgenyfadeev/CNPROG/blob/e560c528524f1c2ad4fbc8c73ee1482693e7b7de/forum/management/commands/send_email_alerts.py