[REF] refactor the code in order to split it in several file

mail_usability/models/mail.py

@@ -0,0 +1,26 @@
+# -*- coding: utf-8 -*-
+# Copyright (C) 2016-2017 Akretion (http://www.akretion.com)
+# @author: Alexis de Lattre <alexis.delattre@akretion.com>
+# License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl).
+
+
+from odoo import models, api
+
+
+class MailThread(models.AbstractModel):
+    _inherit = 'mail.thread'
+
+    @api.multi
+    @api.returns('self', lambda value: value.id)
+    def message_post(self, body='', subject=None, message_type='notification',
+                     subtype=None, parent_id=False, attachments=None,
+                     content_subtype='html', **kwargs):
+        if not 'mail_create_nosubscribe' in self._context:
+            # Do not implicitly follow an object by just sending a message
+            self = self.with_context(mail_create_nosubscribe=True)
+	return super(MailThread,
+            self.with_context(mail_create_nosubscribe=True)
+            ).message_post(
+                body=body, subject=subject, message_type=message_type,
+                subtype=subtype, parent_id=parent_id, attachments=attachments,
+                content_subtype=content_subtype, **kwargs)