add topic_compare to jsk_topic_tools

Adding the tool to compare bandwidths of two or many topics published.

To use this program, run as following:
```bash
rosrun jsk_topic_tools topic_compare.py -h  # show full usage
rosrun jsk_topic_tools topic_compare.py /cam/image_mono /cam/image_color /cam/image_color_compressed ...
```

This program is argued on #298