Minor clean up: Cleans namespaces and adds support for IOInterface to ask question

- Removes backslashes of namespaces
- Replaces CLI question part with the internal utils like IOInterface
 - https://github.com/composer/composer/blob/master/src/Composer/IO/IOInterface.php#L98
- Fixes code style with 'php-cs-fixer --config=sf23 fix .'