[urdf] Change talos_small.urdf to use the smaller STL meshes.

* depends on urdfdom>=0.2.9. does not depend on Catkin
* remove package.xml
* add submodule cmake

NOTE: ASSIMP is angry with the header of the bigger STL files like arm_1.stl

*make talos_description into current package. remove other sub-packages
*Contains srdf file with feet specificities, halfSitting and disabled collision pairs
*Contains urdf file for loading simpler "collision" geometry in visual models.

*Defines the half-sitting position
*Defines common kinematic chains
*Disables "always in collision", "never in collision" and "adjacent" collision pairs after sampling of Configuration Space with Moveit.