Testing

Fixes #74 (closed)

NOTE: This is based on !28 (merged), so that MR should really be merged first.

The current state pretty much lays down a complete CI infrastructure for automated builds and tests, currently using Firefox and Chrome.
Things left to do/consider before this can be merged:

• Implement actual tests
• Consider also implementing unit tests for some functions?
• Also test different languages?
• The testing is currently fairly slow due to the fact that we have to install Firefox and Chrome for each iteration. The solution to that would be to create a docker image with those preinstalled but I'm not sure if we want to put up with the hassle of actually maintaining that…