Changed evaluate to fit_evaluate

Created by: scarlehoff

In order to implement the Genetic Algorithm in n3fit in a very general form, it is necessary to roll back the change I did to evaluate in order to output something similar to what fit so now there are two methods, fit_evaluate, which returns a dictionary with all the required information and evaluate which returns raw the result from Keras' evaluate function.

WIP since I might found some other things that need changing