Add support for multiple losses during training

[george-gca]

Is your feature request related to a problem? Please describe.
My model uses multiple losses during training, and it would be useful if I could visualize each one of them.

Describe the solution you'd like
When sending info to server, it would be nice if a dict of losses (composed by its names and current value) could be provided.

Describe alternatives you've considered
Maybe it would be nice to split the sendLoss function into different functions, like sendLoss, sendMetrics.

Additional context
For cases when working with GANs, that we have two different models with different losses, or maybe even one single model with two weighted losses.