Add chest_xtion camera in urdf file, add calibration of chest camera with respect to ground floor

This commit incorporates the new chest camera in the urdf file. I'm calling it chest_xtion because it's much short than chest_primesense but I can change that if someone objects. This pull incorporates:

* Add chest_xtion in the urdf file
* Calibrate camera with respect to ground floor with calibrate_chest node, store in strands_datacentre
* Launch chest_calibration_publisher node with scitos_state_publisher launch file to publish the height and angle of the camera calculated in calibrate_chest
* The node stops publishing after ten seconds, latest values should remain in tf tree
* To get the latest values you need to have strands_datacentre running before launching scitos_state_publisher or run the calibration node since it will store the values with rosparam

So the question is if this is the right package for these nodes or if we should put them somewhere else. Because calibrate_chest relies on strands_datacentre for storage that's a dependency for building.