Add UML Diagram generation to tests.

This PR is inspired by Aegir provision patch https://drupal.org/node/2143043 to make understanding the OO code a little better.

While working on it's code some issues arose related to drush

- [ ] Can drush handle PRS-0 based drush extensions? What happens if provision needs PSR-0 libraries?
- [ ] Same goes for Drupal 8 PSR-4 modules with drush extensions.
- [ ] Are these diagram only useful in the tests or should we build it differently.

![drush-uml](https://f.cloud.github.com/assets/371014/1645512/3196e544-5902-11e3-9a60-a430778d7508.png)

To test this

- ```composer update```
- ```php tests/UML.php```