output the segmentation as PolygonArray as the result of OrganizedMultiPlaneSegmentation

add ~output_polygon to OrganizedMultiPlaneSegmentation
![screenshot from 2014-05-16 16 50 12](https://cloud.githubusercontent.com/assets/40454/2994505/9d7c02f8-dcce-11e3-9f8e-0676f1c5301a.png)