Update effort limits in PR2 urdf (ros ticket #4557)

[ahendrix]

Currently effort limits are being enforced in the joints by the motor current limits. I would like to enforce the appropriate effort limits in the safety section of the urdf for two reasons:

1. Robots running in Gazebo will also have the effort limits.
2. It will for controllers (and other code) to discover the actual effort limits.

trac data:

• Owner: sglaser
• Reporter: sglaser
• Reported at: Wed Jul 14 16:58:51 2010
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/4557

[ahendrix]

[wim] We already have effort limits in the safety section of the joint. Did you want another one?

{{{

``` ```

}}}

[ahendrix]

[sglaser] Most of the values inside of effort="" are incorrect.

[ahendrix]

[wim] Then we should update our pr2 description. Do we know what the correct values are?