Added optional 3d obstacle avoidance to scitos_2d_navigation

So this pull request doesn't really change anything in how scitos_2d_navigation works, basically you will be able to use it exactly as before, with optional 3d obstacle avoidance. Changes are:

* Provide with_camera:=true to scitos_2d_nav.launch to enable 3d obstacle avoidance.
* The default camera is now chest_xtion, provide camera:=head_xtion to use the one on the head
* New move_base_3d launch file and separate move base parameters in the folder scitos_move_base_params_3d
* Some new nodes to do filtering of the pointcloud for the obstacle avoidance:
  - subsample_cloud to remove noise with a kind of voxel grid: to few points in voxel -> don't add points
  - remove_edges_cloud to remove edges of field of view and remove points close to the camera
* The 3d obstacle avoidance operates on 2 clouds, one for adding obstacles and one for clearing them with ray-tracing
* The noise filtering is done for both
* The points on the floor are only used for clearing, done via threshold on height
* The obstacle adding point cloud has a somewhat reduced field of view to prevent obstacles lingering at the field of view

This commit is made mostly to be able to review the structure of the current work. It seems to work quite good also for moving obstacles now.