Initial commit of Kuka robot based on Model KR210 step file.

The received step file was titled "KR150_180_210_240-2AV400", so these meshes might represent a family of robots, but for now things are specifically referencing the KR210.
There are STL's and dae's in the visual folder because the stl's are oriented "properly" with all z axes going in the world z axis direction, whereas the dae's are rotated 90 degrees. The dae's have color so those are included in the macro.xacro and the urdf with a pi/2 rotation to fix links 2-5 (links 0, 1, and 6 are ok).

@shaun-edwards let me know if you see anything that needs fixing.
@shaun-edwards already mentioned it: `Link1` -> `link_1` (at least, the added underscore has been the convention, if KUKA uses something different, perhaps that should be used here).

Does KUKA use numbers to refer to links / joints, or letters like Motoman?