metrics should be refactored

[jacksalici]

Now the utils package provide also a BinaryMetrics class, but not a BaseMetrics class that can be used in the experiments classes. This would allow a more standardized way to handle returned objects in the validate functions.

[jacksalici]

Maybe the best option is to create a folder inside utils called metrics in which there is the baseMetrics class, as long as all the possible other metrics classes (in this template, just the binaryClassificationMetrics, classificationMetrics, and maybe something more regression oriented)