Enhancement/update meshes

This PR updates the UR5 and UR10 meshes according to ROS-Industrial standards as described here:
http://wiki.ros.org/Industrial/Tutorials/Create%20a%20URDF%20for%20an%20Industrial%20Robot

This included:
- setting the origins of the meshes into the according joint frame
- proper scaling and actual application of position, rotation and scale within the meshes
- removal of additional light and cameras in mesh files
- use convex hulls for collision tags
- remove gazebo materials form URDF description
- unify color and texture of ur5 and ur10

The meshes have been re-worked by Feyyaz Cakir of Fraunhofer IPA. Thank you!

I also re-generated the plain URDF files to reflect the latest updates in the XACRO files


NOTE: The kinematic and dynamic description is untouched by this PR