- removes APNS support
- changes the `django-push-notification` library from the `iskhakov`
fork to the [`grafana`
fork](https://github.com/grafana/django-push-notifications). This new
fork basically just patches an issue which affected the database
migrations of this django app (previously the library would not respect
the `USER_MODEL` setting when creating its tables and would instead
reference the `auth_user` table.. which we don't want)
- add `--no-cache` flag to the `make build` command
**NOTE**
A migration should be applied as follows:
```bash
# remove the four push_notifications tables, which have improper foreign key references
python manage.py migrate push_notifications zero
# recreate the tables with the proper foreign key references
python manage.py migrate
```
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