[ADD] mail_message: added model_id field to provide search by applicatio...

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[IMP/FIX]mail: mail.js: hide 'Mark all read' button, when thread is having all the messages makred as read.

 - Task: https://www.odoo.com/web#id=6824&view_type=form&model=project.task&action=333&active_id=131
 - Pad: https://pad.odoo.com/p/r.JmRhE3JrBVAPrpye
I think the field can be stored, it will simplify its management. Just use a conditional store, based on the model field. This way you won't have to define the fnct_search.