error table sometimes missing stress/virial columns

[bernstei]

I'm no longer getting the stress column in my error table, even though I have stress_weight and stress_key. I also switched to loss="universal", so I wonder if that's the issue. In any case, it'd be nice to have that output back.

[bernstei]

Can we clean up the huge mess of model, loss, and error table, both in terms of including/not including terms (e.g. virials/stresses), and craziness of overriding the user's choice of MAE vs. RMS when you specify certain loss values?

Can we not just have the user specify the terms they want, and the functional form of the loss (e.g. conventional RMS vs. huber), and the error type, and have everything based on that, rather than an explicit list of particular combinations?