[MERGE] pos improvements

addons/point_of_sale/point_of_sale.py

addons/point_of_sale/point_of_sale_view.xml

addons/point_of_sale/static/src/css/pos.css

addons/point_of_sale/static/src/js/db.js

addons/point_of_sale/static/src/js/main.js

addons/point_of_sale/static/src/js/models.js

addons/point_of_sale/static/src/js/screens.js

addons/point_of_sale/static/src/js/tests.js

addons/point_of_sale/static/src/js/widgets.js

addons/point_of_sale/static/src/sounds/error.wav

addons/point_of_sale/static/src/xml/pos.xml

addons/point_of_sale/test/test_frontend.py

addons/pos_discount/__init__.py

addons/pos_discount/__openerp__.py

addons/pos_discount/discount.py

addons/pos_discount/static/src/js/discount.js

addons/pos_discount/static/src/xml/discount.xml

addons/pos_discount/views/templates.xml

addons/pos_discount/views/views.xml

addons/pos_restaurant/__init__.py