Report support vectors of SVM models (update libsvm)

[dbogdanov]

We are currently using an old verion 2.8 and we can update to the newest version 3.21. There does not seem to be any important updates that would change models behavior according to the changelog. However, one very useful feature was added:

• add sv_indices in model structure, so users can know which training instances are SVs

We should be able to provide such information about support vectors back to Gaia model training scripts and log it.