PIM-2613 : use product value interface to replace abstract class
PIM-2613 : use product interface to replace abstract class
PIM-2613 : use product price interface to replace abstract class
PIM-2613 : use metric interface to replace abstract class
PIM-2613 : use completeness interface to replace abstract class
Merge pull request #1868 from akeneo/PIM-2613-product_value_interface

PIM-2613 : prefer interfaces than abstract classes for models