Fully mavenize Nuxeo Content Platform Docker image build

To be consistent with the platform Maven build:

• Move Dockerfile to nuxeo/docker.
• Use pom to resolve the distribution and packages ZIP files as Maven artifacts.
• ...

This should allow to:

• Build the image with packages locally with Maven.
• Replay the Docker build stage of the platform pipeline without depending on a distribution built in nuxeo-distribution/nuxeo-server-tomcat/target by a previous stage.
• ...