The Dockerfile is used currently only for building on Linux. It works pretty well, and it'd be nice to use it for tests too. The .travis.ymlfile is almost identical to the Dockerfile because in the end they do pretty much the same. Using only the Dockerfile would simplify this and avoid code repetition.

I haven't been able to do it because I get really weird messages, though. I need xvfb or similar because Qt requires a x server running, even if no GUI is opened at all.