Add penalty for when the robot has a collision

[rickstaa]

The training might be improved if you add a penalty for when the robot has a collision.

Resources

• https://frankaemika.github.io/docs/franka_ros.html#franka-hw
• https://ros-planning.github.io/moveit_tutorials/doc/visualizing_collisions/visualizing_collisions_tutorial.html
• http://gazebosim.org/tutorials?tut=contact_sensor&cat=sensors

[rickstaa]

This feature was implemented a while back and has been part of the codebase since the commit at https://github.com/rickstaa/ros-gazebo-gym/commit/526a585fae03182f511d8fd997915faad4993021.