Lps 35220 part3

This is the updated implementation of the organization SMDH. As we discussed, I have also added a new method on the BaseStagedModelDataHandlerTestCase class in order to clear the model from the database that has just been exported in order to import it again within an empty environment. I have implemented such method as an empty one for now and I override it when needed (Organization and UserGroup tests for now). But I really think this should be abstract and be implemented by all methods that extends from this base class