adds robotiq urdf from alexg
robotiq hand model was bringing drake to it's knees.  turns out the rbm object was 3.5 GB in memory.  after a painfully slow debugging process, we figured out that it was because the loop joints, and drakeFunction kinematic constraints, contained a copy of the manipulator, which nested into a massive memory alloc.  the stopgap solution is to zap the system constraints for the copy of the rbm that is stored inside the kinematic constraint class.