fix plot training history

[moserle]

• show the history (loss and accuracy) of the training in the fitClassifierDialog
• use tfjs-vis if possible

[moserle]

• The training history is plotted but after the training. Training the model blocks the main tread -> the plot is updated after the training.
• Enhance the plots: add information about the different plots
• Show information about the training progress, e.g. how much % of the data was processed

[moserle]

Official tensorflow.js mnist example: demo: https://storage.googleapis.com/tfjs-examples/mnist/dist/index.html code: https://github.com/tensorflow/tfjs-examples/tree/master/mnist