[CRM] Migrate to new API

- Task: https://www.odoo.com/web#id=10543&view_type=form&model=project.task&action=333&active_id=248
- Pad: https://pad.odoo.com/p/r.qE00VdREVpboKWJp
if `this` was an `id`, maybe we should put `@api.one`, but I'm really not sure about the use of `this`...