[MIG] website_blog: new api migration

- Task: https://www.odoo.com/web?debug=#id=9783&view_type=form&model=project.task&action=333&active_id=131
- Pad: https://pad.odoo.com/p/r.gSXNQBNaLZL5Ausm
Wouldn't this be simplified by using partner recordsets everywhere? Only line 221 doesn't set up recordsets, it could either be browsed or _find_partner_from_emails could return a recordsets, and its other callsites could be fixed.

That aside, I'm not sure _find_partner_from_emails will be correctly bridged to the new API, it takes `cr, uid, id` but the id can be in a different model than the subject, the method may beed to be bridged explicitly.