Enhancement: Run PHP_CodeSniffer on Travis

This PR

* [x] updates `.travis.yml` to run `phpcs` on Travis
* [x] adds an XML configuration for `phpcs`
* [x] removes the dependency on [`fabpot/php-cs-fixer`](https://github.com/fabpot/php-cs-fixer)
* [x] updates `README-GIT.md` in regard to suggested GIT `pre-commit` hook, use `phpcs` instead of `php-cs-fixer`

Let's see how much pain this is going to cause.

/cc @Maks3w