Added PSR-4 autoloader methods in workbench command.

PSR-0 is now deprecated(http://www.php-fig.org/psr/psr-0/).
So by default, we should be using PSR-4 autoloading, and this PR adds it.

I've tested it from console. There are two things coming ahead:
- Ability to create PSR-0 packages.
- Automated testing for workbench command.

BTW, why are tests not written for workbench commands?