RAD-333 Use fabric8io docker plugin
Use fabric8io docker plugin instead of spotify's since it allows to link
containers. This way we do not need docker-compose and can totally integrate
docker into the maven build process.
* use fabric8io docker plugin
* define it in api/pom.xml with skip=true so we can build docker from the root
dir
* configure omod/pom.xml to use the docker plugin
** define the db image (from docker hub) with run properties
** define the radiology image with a link to db
* update readme
* add DOCKER.md
* put DEMO-DATA.md and DOCKER.md into docs/
