This commit removes the strange selection box based on a magic flag and
some strange methods returning a string. Instead just allow to send mass
mailing on all models inheriting from mail.thread using the is mail
thread flag.
Various addons are updated to remove the _mail_mass_mailing class
attribute used to determine mass mailing capability.
We consider people could send a mass mailing on every model inheriting
from mail.thread. It makes no sense to limit it to a given set of addons.
Since saas-3, website controllers use `request.website.render`
to render the template of a web page. This was kept for retro
compatibility. It's time to stop using deprecated stuff.
Same for `_render` method on website.
'json' route don't use `request.render` since
`JsonRequest` has no `render` method.
The unsubscribe URL is used within the `mass_mailing` module,
e.g. in `_get_unsubscribe_url` & `send_get_email_dict`.
Basically, there is the possibility to add the unsubscription
link in the mass mailings while having only
`mass_mailing` installed.
But, the unsubscription route is defined within
the module `website_mass_mailing`.
Therefore, if you added the unsubscription link
within your mailings while not having
`website_mass_mailing` installed, trying
to follow the unsubscription link leaded to
a `404 Not Found` page.
We therefore define the route within `mass_mailing`
directly, which does the basic stuff (the basic
unsubscribe and confirmation), and override this route
in `website_mass_mailing`, where the advanced stuff is done
(the mailing lists list unsubscription and the better
looking page).
opw-669425
Yannick Tivisse