The global DSSTCentralBody force model, which was only a container
for one zonal model and one tesseral model, has been deprecated.

This will allow in a later step finer tuning of both zonal and tesseral
terms. If we had kept DSSTCentralBody, the construction parameters would
have been a huge mess of maxIndices (indeed, even separating zonal from
tesseral will induce constructors with numerous parameters ...)