German language added

I added the German language for you to include in a future MR on the Main Repository.

I am watching this repository to see every change you do so that I can keep up with changes in the translation so that it stays current until it is merged back.

Also: Maybe it would be a good idea to outsource the actual level info
> selector : "bento",
> board: "[]()[]"

back into a levels.js-File since they are independet of the translation but affect the engine instead.