This commit contains mainly code cleaning, docstrings and a small split
for notification tool methods. In this commit we
* make some notification groups variable explicit;
* move the filler of groups into its own submethod to ease being called
from other code (to be used soon);
* fix some strange overrides or code manipulation;
* propagate some additional parameters to ease future commits that will
improve rendering of groups-based notification emails;
* cleanup, fixup and improve docstrings;
This does not change anything from functional point of view, just preparing
further work.
Task-3046371 (Mail: Better Language Support in Composer)
Part-of: odoo/odoo#106177
Thibault Delavallée
c088d5423e