Support contiuous model building on EnvironmentPlaneModeling and add a launch file for footstep planning recogniton

* support continuous model building on EnvironmentPlaneModeling
* add footstep_recognition.launch, which is a specialized pointcloud pipeline for footstep planning

![screenshot_from_2014-10-10 22 46 47](https://cloud.githubusercontent.com/assets/40454/4593845/0424a472-508a-11e4-956d-2dac1be80cb0.png)
![screenshot_from_2014-10-10 22 46 57](https://cloud.githubusercontent.com/assets/40454/4593846/042c0bae-508a-11e4-8f43-0af62eb6eb3e.png)
![screenshot_from_2014-10-10 22 47 06](https://cloud.githubusercontent.com/assets/40454/4593847/042c402e-508a-11e4-89d2-bf4db3f025e1.png)