[jsk_pcl_ros] Supervoxel segmentation

supervoxel segmentation nodelet.
This is a wrapper of `pcl::SupervoxelClustering`

see http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6619108&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all.jsp%3Farnumber%3D6619108 about the paper.

![supervoxel_segmentation](https://cloud.githubusercontent.com/assets/40454/5586105/81e9633c-9105-11e4-93f0-875d0c24ab7e.png)