[IMP] various: Clean stat buttons across all modules.

Purpose
=======

Make them consistent.
Make sure context is correctly set.
Prevent creation when necessary.

Specification
=============

See https://www.odoo.com/web#id=2024467&action=333&active_id=1251&model=project.task&view_type=form&menu_id=4720


for the detailed list of all the requested improvements.

TaskID: 2024467

closes odoo/odoo#34561

Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>