[IMP] [BACKPORT] Mailing lists usability improvements: headers related to mailing lists, use of email queue for notification emails (> 50 followers), archive website template imp and fix. Backport of commit 839815f of saas-5 (PR 502).
Merge pull request #830 from odoo-dev/saas-4-mailing-lists-imp-tde

[IMP] [BACKPORT] Mailing lists usability improvements: headers related t...