The repo now contains a Dockerfile that can be used to build a Docker
image for running the YADG main application and celery workers.

The image will start a Gunicorn instance by default after collecting all
static files and optionally migrating the database.

A celery worker node can be started by using the script in
`docker/celery.sh`. This script depends on a Redis instance which is
used to determine the node id for the worker node. Using this in
conjunction with `docker-compose scale` can dynamically create all
necessary worker nodes to fulfill all queue constraints without the need
for hardcoding them.