Enable Code Climate statistics

[Robbert]

While we already have a lot of lint checks enabled and it does wonders for our code quality, it results only a bunch of negative criticism. We could track statistics over time and show the increase of quantifiable improvements to see the positive side of all those lint warnings.

• Add the codeclimate.yml configuration file

[Robbert]

Apparently it is because dotfiles aren't being validated, because by default glob patterns exclude hidden files.