[IMP] Contract form view : stat button to see all the related invoices

Task : https://www.odoo.com/web#id=10966&view_type=form&model=project.task&action=333&active_id=248
Pad : https://pad.odoo.com/p/r.wL0uJs1oXaRMMjqa

Yay, @xmo-odoo is agreed :-)