[Accounting] revenue recognition

- Task: https://www.odoo.com/web?#id=6357&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.n8sCRDTVK3sqmxsV
Something like sum(line.amount for line in assert.depreciation_line_ids for assert in assets) could simplify this code I think.