Set compute3Dcentroid last component to 1

When computing a centroid in an `Eigen::Vector4f` the last component should be 1 because the centroid is a point; not a direction.

For the moment the last component of the computed centroid is 0.
This means that if a 4x4 matrix is used to transform the centroid, only the rotation will be taken in account. (not the translation)
This is the behavior when transforming a direction; the centroid is not a direction.