CLN: Move vak.common.trainer into frame_classification / have per-model family trainers

[NickleDave]

It doesn't make sense to have the trainer we use only for frame classification models in vak.common.trainer

We want per-model family trainers. Not sure what the package structure / API should look like

Currently for parametric UMAP we define a function inside vak.train.parametric_umap I think. We could convert parametric_umap and frame_classification to packages (package-inception) then have a module with a helper function to get_trainer