[ADD] Add a new graph view in mailing list contacts to track list subscr...

...iptions and unsubscriptions + custom filters provided

- Task: https://www.odoo.com/web?debug=#id=9618&view_type=form&model=project.task
- Pad: https://pad.odoo.com/p/r.Lgn9WTUeZrpgZeSZ
Moreover, you should link this method in the create and write, because automatic unsubscription from mailing lists using the controller is likely to write on the record and avoid using the form view.