Reformat project with clang-format
- Add a clang-format file for the correct format to the project according to the guide lines in TODO.txt: - Klammern von Bloecken beginnen immer in neuer Zeile - einruecken von 4 Leerzeichen (kein Tab) - Reformat the whole repo: Best when no other large works are in progress, as the merging then may result in a lot of conflicts - (optional) Add check for correct format to CI
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