Improving adversarial_validation function

[atselikov]

Would be nice to add a new list of dataframes names. Maybe the user has three 3 dataframes(datasets)[trian, validate, test] and the user interested in applying the test between validate and test, the user should be able to do this by applying the following:
adversarial_validation(dataframes_dict, ignore_columns, datasets=["validate", "test"]) or
adversarial_validation(dataframes_dict, ignore_columns, datasets=["train", "test"]) or
adversarial_validation(dataframes_dict, ignore_columns, datasets=["train", "validate"])