Target visualizer

rviz plugin to visualize PoseStamped as Target Mark


![screenshot from 2014-07-16 18 19 16](https://cloud.githubusercontent.com/assets/40454/3596791/6c6323f0-0cca-11e4-9399-27db1798c25d.png)

![screenshot from 2014-07-16 19 13 44](https://cloud.githubusercontent.com/assets/40454/3597458/042e672e-0cd2-11e4-800d-ff53d46cbb8f.png)