Fixes: https://github.com/ckan/ckan-docker/issues/104
Adds `--chown` flag to `COPY` command in PostgreSQL Dockerfile to ensure that initialization files can be executed by `postgres` user.
- Update database user names and passwords
- The CKAN database is created with a new SQL script in the docker-entrypoint-initdb.d/ directory
- Remove host port for CKAN container
- now has a front-end network for NGINX and a back-end network for the rest of the containers, plus NGINX
