Original code taken from:

https://github.com/fetchrobotics/fetch_ros

Modifications:

 * Comment out `bellows_link` and `bellows_joint`. You can push off the ground using this strange thing!

 * Set moments of inertia of `r_gripper_finger_link` and `l_gripper_finger_link` to non-zero.

 * Set moments of inertia of `base_link` to zero, except for Z-axis, to disable rotation other than around Z axis.

 * Added `<gazebo reference="head_camera_rgb_optical_frame">` for camera, turn `head_camera_rgb_optical_frame` 180 degrees as camera was facing backwards.

 * Spheres are now collision shape for wheels (fixes jumping).

 * Boxes for fingers collision shape.