Robotiq problems solved: collision checking in MoveIt was not disabled
for Robotiq joints. UR5 XACRO file now has some parameters that can be
configured to alter the simulation: "show_underactuated" includes the
outside "finger" links in the Robotiq gripper, and "gravity" controls
whether or not the gripper is affected by gravity. We found problems
with the gripper when gravity was enabled.