add StereoSGBM and it can be chosen from dynamic_reconfigure

support `cv::StereoSGBM` in `stereo_image_proc/disparity`.
* add several parameters to dynamci_reconfigure parameters for StereoSGBM.
* the algorithm for stereo computation can be also chosen via dynamic_reconfigure

![screenshot_from_2014-08-25 18 32 13](https://cloud.githubusercontent.com/assets/40454/4028271/b25b6022-2c3a-11e4-96b3-06a092509a92.png)