Move cakephp-codesniffer into require-dev, use CakePHP standard

Coolio.

It's irritating when github is being derp and the phpcs run is delayed or aborts downloading dependencies that aren't required - especially chunks of phpunit which is ofc huge. That was the original motivation for _not_ installing dependencies for the phpcs run (though at that time phpcs wasn't a dependency, so it really was of no benefit).

Speaking with jose I think we've collectively decided to require-dev our cs standard and phpunit on all projects (except app) now.