[IMP] project : mailgateway: add to and cc as followers of the newly created task

Task: https://www.odoo.com/web#id=8881&view_type=form&model=project.task&action=333&active_id=131
Pad: https://pad.odoo.com/p/r.Phmae3XO8sAcbUVR
You should use tools.email_split() I think.