Allow support of Docker registry version 2.

[bgaillard]

This PR adds the following features and improvements.

• Upgrade NGINX to last version ;
• Allow to proxy Docker registry version 1 and version 2. Default is now version 2 (see https://docs.docker.com/registry/spec/api/) using a DOCKER_REGISTRY_VERSION Docker environment variable ;
• Fix shell script to not output any ShellCheck error (see https://github.com/koalaman/shellcheck) ;
• Add new build.sh script to easily build a new Docker image ;
• Add new publish.sh script to easily publish a new Docker image.