[ADD] base: add OPL-1 module license

This allows people to create modules under the 'Odoo Proprietary
License' version 1.0 rather than having to rely on the rather vague
'Other Priorietary' license.

The text of the license can be found at:
https://www.odoo.com/loempia/static/examples/LICENSE

This should already have been in Odoo 9 but was mistakenly left out.

odoo/addons/base/module/module.py

@@ -261,6 +261,7 @@ class Module(models.Model):
         ('LGPL-3', 'LGPL Version 3'),
         ('Other OSI approved licence', 'Other OSI Approved Licence'),
         ('OEEL-1', 'Odoo Enterprise Edition License v1.0'),
+        ('OPL-1', 'Odoo Proprietary License v1.0'),
         ('Other proprietary', 'Other Proprietary')
     ], string='License', default='LGPL-3', readonly=True)
     menus_by_module = fields.Text(string='Menus', compute='_get_views', store=True)