Add gp7 opw

[cjue]

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

[cjue]

Sidenote: somehow all of the technical drawings and tables I could find for the GP7 are missing the height offset from base_link to link_1_s. According to the current URDF it's identical to the values for GP4 and GP8, which sounds reasonable.

https://www.yaskawa.eu.com/Global%20Assets/Downloads/Brochures_Catalogues/Robotics/MOTOMAN_Robots/GP-Series/Flyer_Robot_GP7_E_10.2021.pdf

[EricMarcil]

@cjue I'm surprise that the dimension is missing from the drawing. I can confirm that the distance is 330mm. If you ever need to look-up that distance for other robots, the MotoSim manual has them all listed in the chapter 15.9: MotoSimEG-VRC manual

[cjue]

Thank you for that hint