[FIX] res_partner: fixed display of simplified partner form view (image and fields display was messy)
[IMP] point_of_sale: track session logins

the pos session now keeps track of the session logins, and that number is
included in in the order reference. This prevents orders generated in parallely
created sessions from having the same reference, and also helps reduce fraud.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64