Add the purpose to successfully constructed learnblock.

cml/domain/construction.py

@@ -128,6 +128,9 @@ class Constructor:
                         labels = trained_model.get_labels()
                         labeled_learnblock = learnblock.set_labels(labels)
                         labeled_learnblock.n_cluster = cluster_number
+                        purpose = "{}{:02}".format(ml_model.abbreviation,
+                                                   cluster_number)
+                        labeled_learnblock.purpose = purpose
                         yield labeled_learnblock
 
     def _construct_procedural_knowledge(self,