Docker Deployment Changes

With this update the whole docker stack has been reworked to make installing and running this application easier. Many thanks to @h4llow3En for providing the initial pull request and lots of help.

To migrate from previous Version:

• backup the database and probably best the whole installation directory
• remove all project files except data and configuration using
  rm -R -v !(".env"|"mediafiles"|"postgresql"|"staticfiles"|"docker-compose.yml")
• choose one of the provided docker examples
• start the container using docker-compose up -d

Changes

• smaller install size due to optimized image
• faster and easier update due to image based installation
• automatic migration and static file collection on each restart
• simplified superuser creation