Add Twig ToolbarExtension to render administration toolbar

This Twig extension will allow to render parts of Drupal administration toolbar into a Symfony Twig template.

Here is the toolbar rendered:

![capture decran 2014-05-28 a 11 27 03](https://cloud.githubusercontent.com/assets/103900/3102687/5ecb0cb8-e64a-11e3-884c-bb2a43b16762.png)