add new nodelet: SLICSuperPixels, a nodelet to compute superpixels based on SLIC method

add nodelet to compute slic-superpixels.

it uses the code here: https://github.com/PSMM/SLIC-Superpixels

the code is super experimental, it's only available on hydro/catkin and no output is available on ROS.
just showing the image.
no parameters are configurable.

![screenshot from 2014-08-01 20 05 26](https://cloud.githubusercontent.com/assets/40454/3778046/09f7035e-196c-11e4-916e-2a1d3fedbe3d.png)