Integrate PHPCS

PHPCS or PHP_CodeSniffer is used to inspect your code against a set of rules to detect code style violations.
This is used to keep all code in ones repo uniform.

More inforamation:

- https://github.com/squizlabs/PHP_CodeSniffer

Refernce/example:

- https://github.com/orca-services/cakephp-heartbeat/blob/cakephp-3.x/phpcs.xml.dist