Trainers and formatters

[JamesOwers]

In general I think it's bad for usability for the Trainer classes to expect a weird formatter dictionary. I think we should look over the formatters and make them simpler / more general.

[apmcleod]

Related, it's unclear to me how general the trainers are. Probably, people creating their own models will just write their own training function to train how they like (at least, that's what I would do, since it's code I have written elsewhere before anyways). So then if the trainers are mainly for our baseline models, I think it's ok to have the format dict there, but we can discuss.

[JamesOwers]

The thing to consider first is whether to use pytorch lightning