[accounting] New API migration - WORK IN PROGRESS

- Task: https://www.odoo.com/web/#id=9955&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.Uy4wEA7I4G4GwPaU
No, this branch contains lot's of re-factoring following all the instruction of Accounting Road-map Version 9.0 (Phase I) and also conversion to new API.