Build docker image withing CI rather than within Quay.io

So far only try to run docker build to see what happends.
If that is working then the built image will have to be pushed to the docker repo.
add docker push to docker repo
login to configured repo instead of default repo
added quay.io status badge
Build Docker image once, tag and push several times

Now building Docker image once only.
Then tagging and pushing with version, branch and :latest.
Also renamed GIT_BRANCH to BRANCH since I got confused all too often with this.
fix missing if end
add $ in front of commands echoed with obfuscated password
Merge branch 'add_docker_build_to_circleci'