Integrate with Travis-CI and Docker Hub

[vsimko]

Expected behaviour

The repository should use Travis-CI for continuous integration. During the build phase, the docker images should be uploaded to dockerhub, so that people can pull the images without building them.

Actual behavior

Currently, the user has to:

• clone the repository
• run maven build
• run docker-compose which builds the images in the background

See also https://github.com/biggis-project/biggis-infrastructure how this can be done.

[vsimko]

I've just activated build for this project on travis and a dummy .travis.yml file.