[DDC-3205] #1120 - metadata info command

Supersedes #1120 - see DDC-3205 (http://www.doctrine-project.org/jira/browse/DDC-3205)

![preview](http://marco-pivetta.com/screen/caps/9a3a9f.png)
I just wanted to avoid that `$this->out` and `$this->output` from being mutable local state :-)