Use phpcs instead of php-cs-fixer

On the main ZF2 repo, changes in the last 1-2 months to php-cs-fixer have deviated from PSR-1/2, and performance of the tool has degraded to the point that it consistently times out builds. As such, we're moving that repo to phpcs -- and this repo should do the same as well.

This patch removes php-cs-fixer as a dev dependency and adds php_codesniffer; additionally, it fixes several CS issues flagged by phpcs.