Initial commit of KUKA KR120 support package

Added support for the KUKA KR120 R2500 PRO manipulator
Meshes are based on the Unigraphics files found at http://www.kuka-robotics.com/res/sps/8ba89f50-3ccd-4361-9b9a-60bdd0662ac6_KR120_R2500_pro.prt.zip
Note that the rotation directions of the KUKA manipulators are different than e.g. the ABB manipulator. For joint 1 this is implemented using <axis xyz="0 0 -1"/>.
No the `origin` has a z-translation component != 0. Looking at the specifications, I believe the translation from `joint_1` to `joint_2` is [0.35, 0, 0] (but I might be confused, as `joint_1` is at 0.2156, which is 0.675 - 0.4594).

I would have expected `joint_1` to be at [0, 0, 675], then `joint_2` at [0.350, 0, 0] (relative to `joint_1`), etc.