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"/>.
Okay. Shall I change the origins to be

joint_1: `<origin xyz="0.0 0.0 0.675" rpy="0.0 0.0 0.0"/>`
joint_2: `<origin xyz="0.350 0.0 0.0" rpy="0.0 ${PI/2} 0.0"/>`
joint_3: `<origin xyz="0.0 0.0 1.150" rpy="0.0 ${-PI/2} 0.0"/>`
joint_4: `<origin xyz="1.0 0.0 -0.041" rpy="0.0 0.0 0.0"/>`
joint_5: `<origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>`
joint_6: `<origin xyz="0.0 0.0 0.0" rpy="0.0 0.0 0.0"/>`
joint_6-tool0:  `<origin xyz="0.215 0.0 0.0" rpy="0.0 ${PI/2} 0.0"/>`

and update the meshes accordingly? This will make the origins correspond to the kinematic parameters found in the file $machine.dat on the KUKA KRC4 controller.