FSI3D: check angular velocity

[tommy-engels]

In the insect module, we had issues with the angular velocity, which was set to
rot = (/ alpha_dt, phi_dt, theta_dt /)
or something like that, not exactly this line.
in the FSI3D module, we also allow rotation of the relative system in the same spirit, but we need to revise the angular velocity; it is not used currently.