Model RG2 gripper properly as four revolute joints for each finger (1 active + 3 passive)

[AndrejOrsula]

As the title says. Current simplification utilises 1 active revolute joint, therefore, 3 more passive joints need to be added (1 at hand, 2 at fingers). This also means that the mesh needs to be split into 3 sub-meshes (both .stl and .dae now use disconnected pieces, so that's easy to do.)

Maybe a plugin needs to be developed that will be mirroring the joints (instead of simulating the physics behing them).

I tried to achieve it, but I instead created a possessed UR5.

possessed_ur5.mp4

Simplification works for me, so I am freezing this issue for now.