Complete gridmap with statically defined polygon

* pink -- GridMap build by sensor and plane detection
* grey -- Completed gridmap with pre-defiend polygon (blue line) for occlusion

![screenshot_from_2014-10-08 21 05 44](https://cloud.githubusercontent.com/assets/40454/4558733/4a975ed4-4ee3-11e4-9692-57186fc2d480.png)