Modify the plane of soft contacts in .bioMod

[Ipuch]

One could be interested in modifying the ground plane of contact in the global frame. For now, the point plane is (0, 0, 0) and the normal of the plane is (0, 0, 1).

Here is a list features that could be integrated :

1. The plane point associated to the plane of contact (easiest, modifying the altitude of the contact)
2. The normal vector of the plane of contact (need to transform the computation into the plane's frame)
3. The segment in which the plane is located (need to add another transformation into the segment's frame)