Face detector visualization

visualization of `people_msgs/PositionMeasurementArray`

movie: https://www.youtube.com/watch?v=u2WXZ0Rydtg&feature=youtu.be
![screenshot_from_2014-08-12 23 09 22](https://cloud.githubusercontent.com/assets/40454/3891453/2167f888-222a-11e4-81de-c1e9c85bf374.png)