[ADD] pos_pms_link: Links POS orders with PMS reservations

[Vicenteagf]

Hi there, this module allows the following:

• Add pms reservation service lines as pos.order.lines.
• Mark pos.orders as paid on pms.reservation (adding pos.order.lines as pms.service.lines in the reservation).

Check it out and let me know if something is missing or wrong.

Thanks!