Inconsistent indentation and trailing whitespace

[PJungkamp]

Many configuration files (both json and conf), as well as lua/txt/... files are still idented using tabs and often contain newlines.

• Use the same indentation style for both .json and .conf files and apply it consistently to our current files in etc/.
• Unify spaces vs. tabs project wide.
• Remove tabs in .cpp/.hpp file comments.

@stv0g What is your opinion on this?

[stv0g]

I think its a good idea. But I honestly dont want to spent more time myself on code maintenance for a few weeks. The REUSE and clang-format stuff was enough :D

If you like, please feel free to go ahead :)