Replace StyleCI with PHPCS

StyleCI needs a pretty long time to get compatible with new PHP syntax features and/or versions.
To don't fail the CI until SCI is up2date we should switch to PHPCS which upgrades faster.

We could also install https://github.com/tighten/duster but should use the Laravel preset: https://gist.github.com/laravel-shift/cab527923ed2a109dda047b97d53c200 (possible PR to duster as new preset).