PURPOSE
Reorganize addon according to guidelines, helping finding and updating
SPECIFICATIONS
Reorganize templates in order to see a bit what's going on here. Notably split
subscription (opt-out, blacklist) from management (view, reporting) templates.
Reorganize controller code by main section in order to separate a bit various
code purpose.
This commit contains only file split / renaming and code move.
Task-2864264 (Mass Mailing Module Reorganization)
Part-of: odoo/odoo#92509
Thibault Delavallée
f446e54cbd