Basic Ranking - Predictions Histogram Distribution

[steven-ja]

• An histogram plot of test predictions is added at the end of the evaluating section.
• More training epoch are used
• A smaller learning rate is adopted
• An EarlyStopping callback on validation data is employed.

@MarkDaoust

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[MarkDaoust]

@maciejkula, I like this change. Can you take a look and merge?