[ADD] [7.0] 'pos_select_customer' module

Propose for merge a module that allow user to select customer in point of sale front-end module (7.0) of odoo.
See description file to see functionnalities and limits.

Old MP: 
https://code.launchpad.net/~sylvain-legal/openerp-pos/7.0_pos_select_customer/+merge/228826