Docker Compose setup for Python 3 and CKAN 2.9+

- rewritten to be more in line with how the OKFN Docker is setup
- Python 3
- CKAN 2.9 (Official version)
- Images are based on Alpine Linux
- Images will be pulled from DockerHub
- will also include a Dockerfile to build CKAN images locally
- Include uWSGI as the entrypoint to CKAN controlled by supervisor
- Include a new NGINX image/container
- Both a Production and a Development version (like OKFN)
- set up automatic builds using Travis / CircleCI
- Migrate to a new repo
- Make sure previous CKAN versions can be taken care of

Review the requested Docker Compose setup, Dockerfile, production and development variants, and the proposed uWSGI, supervisor, and NGINX containers. Check how the OKFN Docker setup and CKAN 2.9+ images are organized first; completion would require an agreed repository migration, local builds, image publishing, CI builds, and support for previous CKAN versions.

Written by the indexing model from the issue text.