Fix blending decoupled cv (#282)

* Update __init__.py

Exposing  ClassifierBaseScoreType so kits can use it.

* Update testing.py

rampwf/utils/testing.py

@@ -222,7 +222,8 @@ def blend_submissions(submissions, ramp_kit_dir='.', ramp_data_dir='.',
     foldwise_best_predictions_test_list = []
     for fold_i, valid_is in enumerate(valid_is_list):
         print_title('CV fold {}'.format(fold_i))
-        ground_truths_valid = problem.Predictions(y_true=y_train[valid_is])
+        ground_truths_valid = problem.Predictions(
+            y_true=y_train, fold_is=valid_is)
         predictions_valid_list = []
         predictions_test_list = []
         for submission in submissions:
@@ -241,7 +242,7 @@ def blend_submissions(submissions, ramp_kit_dir='.', ramp_data_dir='.',
                 problem, data_path=ramp_data_dir,
                 input_path=fold_output_path, suffix='test')
             predictions_valid = problem.Predictions(
-                y_pred=y_pred_train[valid_is])
+                y_pred=y_pred_train, fold_is=valid_is)
             predictions_valid_list.append(predictions_valid)
             predictions_test = problem.Predictions(y_pred=y_pred_test)
             predictions_test_list.append(predictions_test)