Configure travis build to deploy to docker hub

[chclaus]

It would be nice to deploy releases automatically to docker hub.

All commits, tagged with a release version should automatically be pushed to docker hub with respect of the current tag / version.

More informations can be found here:
https://docs.travis-ci.com/user/docker/#Pushing-a-Docker-Image-to-a-Registry

[mpizala]

I would like to take over this.

[chclaus]

Awesome! 🎉