Graphvizpresenter

![get_preview 1](https://cloud.githubusercontent.com/assets/5455804/4033732/d887a302-2c7e-11e4-8fd3-bdedb3f73568.png)
![get_preview 2](https://cloud.githubusercontent.com/assets/5455804/4033733/d88ea576-2c7e-11e4-9f87-d96604995f1a.png)
![get_preview](https://cloud.githubusercontent.com/assets/5455804/4033734/d8999d32-2c7e-11e4-8eb8-1b61f4cd2fce.png)