[IMP] energy_selfconsumption: integration invoicing

This is the Trello card

In this branch we worked on the last point of the requirements:

1. Changing the relationship between contract template and self-consumption so that contract template is linked to the product.
2. On the other hand, the obtaining of information is modified so that when the project is activated, contracts are created taking the values ​​stored in self-consumption.

energy_project/models/__init__.py

@@ -3,4 +3,3 @@ from . import project_type
 from . import inscription
 from . import reseller
 from . import supplier
-from . import contract