use null space for aligning orientation

refer to this issue
https://github.com/jsk-ros-pkg/jsk_roseus/issues/133#issuecomment-68030463

![screenshot_from_2014-12-27 18 14 16](https://cloud.githubusercontent.com/assets/4415085/5561097/3327f990-8e01-11e4-906b-aee892d02389.png)