Initialize v18 branch

Rename *_usability modules to *_usability_akretion

hr_contract_usability_akretion/models/__init__.py

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+from . import hr_payroll_structure_type

hr_contract_usability_akretion/models/hr_payroll_structure_type.py

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+# Copyright 2021 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 fields, models
+
+class HrPayrollStructureType(models.Model):
+    _inherit = 'hr.payroll.structure.type'
+
+    active = fields.Boolean(default=True)