Decimated and converted to STL ur5 collision meshes.

This is a workaround for a bug in moveit which I haven't solved yet: https://github.com/ros-planning/moveit_core/issues/202

In any case, these models much more closely match the geometry of the robot since they are not convex.  I did "decimate" them in Blender to reduce the polygon count to make collision checking faster though.