PURPOSE
Clean organization of templates in odoo apps: mail.template records in data,
qweb templates (views) used directly in code, notably using post with view.
Purpose is to ease future improvements in posting based on templates.
SPECIFICATIONS
* move those templates in their own file to ease their discovering and
maintenance;
* put them into data (as those are not views even if it contains qweb)
* guidelines are now :
-> Qweb templates should be in data/mail_templates.xml;
-> mail.template records should be in data/mail_template_data.xml;
* put their declaration in no update when not done if template has no
technical code or complex dependency on underlying code;
* move found mail data (mail.message.subtype or mail.activity.type) records
in a mail_data file that should contain only "core" records linked to mail;
LINKS
Task ID-2375767
COM PR odoo/odoo#61814
ENT PR odoo/enterprise#14775
UPG PR odoo/upgrade#1936
