[FIX] web: remove enforceFocus method from bootstrap modal since it is conflicting with other non bootstrap element

This method trigger the focus event when clicking inside the modal, causing a blur event on other widgets resulting in unwanted problem. Typical case is for the jquery datetimepicker where we try to open a select element which will close right after.
[FIX] website_sale: check the first product variant radio button in variants list by default to avoid users to click on Add to Cart without choosing any variant
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-win32