POS is loading all partners, not only customers

Hi,

Adding domain to res.partner model, so POS only loads "customers"
[point_of_sale] Domain functions to literals

Replaced domain functions with literals where there are only constants
Merge pull request #3803 from TheCloneMaster/patch-7

POS is loading all partners, not only customers
[FIX] hr_attendance: use float division for worked_hours field

Used to be rounded to integer while the field is a float.
Fixes #3526
[FIX] sale_layout: set 0 as default value for categ_sequence

Otherwise, in some cases, the categ_sequence can be set to null, which is not ordered the same way than 0, and you won't be able to sort lines with null and 0 as categ_sequence between each others
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32