[META] phase 3

[oliverklee]

• [TASK] Provide the code language in markdown files #38 Provide the code language in markdown files
• [TASK] Test with both latest and oldest dependencies #39 make sure everything is fine both with the lowest as well as highest version of the dependencies http://naderman.de/slippy/slides/2017-07-13-T3DD17-Composer-Best-Practices.pdf
• make the project structure more similar to the default Symfony project structure