Analysis callback and changes to allow categorical with two options

There are many changes here. The most important are:

• We provide the option to provide a callback to the generator. In that case, the ground truth values are computed. To implement this, I had to also improved the way the errors and loss evaluate are calculated. #123
• For evaluate generation and evaluate training, we can now specify the range where the bins are obtained.
• Additional options for the generation_scatter plot.
• Adding more options for the loss and loss evaluate, to avoid reduction for example. Also, evaluate losses for ordinal and categorical.

And many more, to be described later.