Add gazebo_ros_control PID gains
Tuned manually to make movement via the teleop interface behave well
Wheels still unspecified because they cause the robot to collapse
Use effort joint interface for the gripper so that gripper contacts are well simulated

Removes most of the instability in simulation behavior when lifting objects

Makes tipping behavior in simulation more plausible
I assume that the mass of an assembled base is at least this heavy, given that the robot is around 50lbs total

This better matches the physical robot, though this interface doesn't handle the virtual joints that the robot uses

This plug in is a modified version of the original ros_control plugin and that plugin's "default hardware plugin" (confusing, I know)
The modified model plugin provides a /runstop service to match the real robot's driver, and hooks this up to ros_controls existing estop implementation
The modified hardware plugin provides the mode switching services that the real robot has (mocked for now) and publishes joint states that include the virtual joints used by the real platform. The wrist extension joint behaves the same as the driver implementation. The rotation and translation joints aren't hooked up yet, and it may be difficult to provide their functionality without forking the actual "follow_joint_trajectory" implementation, which expects only joints that are present in the URDF
Mirror the real platform setup and use a joint state publisher node to republish the subset of joints that match the URDF