When we subclass LightningModel it seems to break logging, see #726.

I am at least able to get better logging -- still does some weird things -- if I remove all the magic sub-classing of vak.models.base.Model and instead define model families that each separately sub-class LightingModule, e.g. FrameClassificationModel(lightning.LightningModule).

This actually can be fine for us; we define a per-family class, and we refactor the logic we have now for converting definitions into models such that it instantiates the components of a model and then passes those components into the model-family class when instantiating it.