More style fixes

This is the second part of my crusade against non-standard code style; the first part being #476.

There are two reasons why these changes were not in #476:

1. Rubocop got updated with a lot of new checks, and this PR ensures we adhere to the guidelines set forth in that new Rubocop.

2. I got over the attachment to my personal preferences (such as TODO’s not being postfixed by a colon).

I will probably squash this PR into a single commit, since it gets quite noisy otherwise.
I did started reviewing the "Standard" rubocop is based upon, some of the rules are just conflicting, some make no sense, I'm not sure blindly following all rubocop rules is good, but I also do not like the default shell formatting (which makes code harder to read)