Coding Style

[dey4ss]

As we've seen here, the inconsistent use of tabs/spaces for indentation causes issues when reviewing PRs and is not nice in general.
Additionally, the tab/four space indentation is not in line with the astyle.options in the project root.
I suggest discussing the preferences in this issue. Afterward, I'm going to apply them in a new PR.

[Bensk1]

Good point. How about aligning it with the style used in hyrise/hyrise?

[cdmh]

It seems .gitconfig can be used for automatic conversions. I've never tried it, though
https://stackoverflow.com/a/14759913/198083