[WIP] - Adding ListenerDebugCommand

There are 2 things in this PR
* A valid `composer.json` after passing the `composer validate` command
* The ListenersDebugCommand, which is a copy of the one used by the bundle since I'm not sure the command from the bundle would work adding it here https://github.com/egulias/DrupalAppConsole/blob/master/bin/console.php#L35

If this first implementation work, I can try requiring the bundle and using that command instead of copying the code.

@dmouse @jmolivas I would much appreciate if you can test this, I don't know Drupal :)
Drupal 8 is now using phpunit/phpunit=4.1.*