Task #1909424
The mass_mailing module used a lot of JS "include" to override
the behavior of the kanban view and the html_frame widget.
This commit cleans the overrides by using proper inheritance with "extend"
instead of "include".
It also slightly changes the current behavior of the mass_mailing kanban view
to disable the drag and drop feature only when the view is grouped by "state" or "email_from".
(Before this commit, the drag and drop feature was disabled for ALL fields).
closesodoo/odoo#29452
Aurélien Warnon
8b54088cd2