add nodelet to publish static jsk_pcl_ros/PolygonArray with timestamp synchronized with the pointclouds

add new nodeelt StaticPolygonArrayPublisher to publish the static jsk_pcl_ros/PolygonArray with the timestamp synchronized with the pointcloud.

It must be important to estimate "Ground".

![screenshot_from_2014-06-02 20 48 25](https://cloud.githubusercontent.com/assets/40454/3146744/7f0ff69a-ea4c-11e3-8a30-fe8da1760814.png)
![screenshot_from_2014-06-02 20 48 56](https://cloud.githubusercontent.com/assets/40454/3146753/84807122-ea4c-11e3-942a-aa95d13b2b07.png)