Allow running cleery in Docker

See merge request !537

Add support to build tables and forms for executing actions for multiple objects

Closes #390

See merge request !502

[Docker] Use `SELECT 1` to wait for database

See merge request !535

This removes the need to have host and port as environment
variables (we might get it in a YAML file from a K8s ConfigMap, or
some such). Also, it ensures that the system answering is a database
rather than an IoT Waffeleisen with a bad taste in port selection.

Add Redis password to URL setting as well

See merge request !532

The Celery broker URL requires the password to be passed directly

[uWSGI] Make serving of /static configurable

See merge request !528

Make data checks compatible with non-optional Celery

See merge request !509

[Docker] Fix runuwsgi command-line

See merge request !527

Fix migration naming to adhere our naming rules

See merge request !526

[Docker] Rewrite entrypoint

See merge request !525

[Docker] Run pre-boot tasks in correct order

See merge request !523

Remove unnecessary Celery options

See merge request !524

After all, it is not an entrypoint anymore

En passant, this removes the need to force the entrypoint away if
wanting to spawn a shell in the container

Celery can now be started together with uWSGI if one wants to do that

This reverts commit cedf3588.

The database needs to be migrated before compiling SCSS, as the SCSS
references a site preference.