Purpose is to try to have code easier to read and to update by having a
common way of sorting / writing code. Reorder some fields definitions and
dictionaries, update docstrings, ... in mail applications or when invoking
mail thread API.
Additional stuff worth noting here
* add some tagged in tests helping debugging / choosing tests to execute;
* in a test about mail generation with server action: correctly check
body_html field, not body which comes from the mail.message inheritance
(currently filled due to a side effect but actual field to check is the
html one);
* add same check on input for ``_render_template_qweb`` as done on other
rendering methods (even if rendering on [False] should be supported);
* move code translation update from specific tests into main test class
(code update due to new translations, followup of odoo/odoo@f8c2b02abe);
Some test linting done here
* reorder mail_render tests, remove some duplicated tests;
* reorder mail_template tests, remove some duplicated tests;
Task-2710804 (Mail: Clean MailThread Posting API)
closesodoo/odoo#106025
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>