Input normalization

[dschodt-lanl]

Add helpers for input normalization (e.g., z-score normalization of each channel) before passing through networks.

[galegozi]

Would it be better to normalize when computing loss? It may make sense to only normalize for loss computations...

[dschodt-lanl]

Would it be better to normalize when computing loss? It may make sense to only normalize for loss computations...

I think it's worth trying both approaches since they have differing pros/cons.