Add GP8 OPW parameters

[cjue]

• add opw file
• fix link2 collision mesh
• add flange link
• update reference documentation
• minor fix for velocity limits

[gavanderhoorn]

@cjue: I submitted isys-vision#6 to add 132d728. Please review and merge.

[gavanderhoorn]

Is this a downsampled version of the visual mesh?

(just noticed the visual mesh is 1MB+. Not sure what happened during the review when that was initially contributed ..)

[EricMarcil]

That might have been from a 3D model that included a lot of internal elements which makes if harder reduce but still keep details. I should be able to generate new .dae model by converting MotoSim models that are already reduced.
@gavanderhoorn Do you want me to do it on this PR, or it's probably better to create a separate PR?

[gavanderhoorn]

No, no need.

It's already in the history of the repository, so adding a newer version will not reduce the total size.

[gavanderhoorn]

Marking as requested changes.