[ADD] url shortener & mailing campaigns

- Task: https://www.odoo.com/web/?#id=8277&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.FSooTwZp4c2NBwbi
Actually as it is an inheritance, no _description is required, it will take the one from the parent.