[FIX] mail: invite: use proper translation terms
[FIX] mail: invite: use proper translation terms

Fix translation placeholders in invite wizard, to make them easier to
understand for translators. Also rework the message generation code
to ensure proper XML structure.

spadae22/odoo,spadae22/odoo,spadae22/odoo,spadae22/odoo,spadae22/odoo,spadae22/odoo,spadae22/odoo