Adjust how we handle persistent models

[dgaviola]

Now that we removed the classes PersistentModel and PersistentComponentModel, we need to make a few changes:

• When a new model in the Data node, we will assume is a persistent model, so we should ask for the data source and we should automatically set the id field of type UUID and with the PrimaryKey decorator.
• When creating a composition model, we also have to add the owner field with the OwnerReference decorator.
• We need to take this considerations in the refactorings.