Add more training metrics / visualization and make confusion matrix have more detail

[ykevu]

For the in-browser training feature, we have a visualization of cross entropy loss over training epochs; however, training metrics such as precision, recall, and others (consult Julie / Dave) can be helpful to calculate and visualize plots for as well.

Additionally, the rendered confusion matrix also still has some issues:

1. Probably cannot visualize handle case with many cell types
2. Does not give information on exact counts (normalized), which should be an option for the user to view, perhaps on hover.