UR10 URDF Update + Fixed Link Lengths

This updates the UR10 model description to one which is based on Collada meshes.  Furthermore, the kinematic description is modified to rely solely on Denavit-Hartenberg parameters found in urcontrol.conf.  Currently, the kinematic paramaters in the UR10 urdf disagree with those in the ur_kinematics/ur_kin.h files.

Hopefully this will fix #74 and #4.