[FIX] website_sale: auto-confirm free orders upon cart validation

Orders are normally confirmed when the payment transaction
is processed, but there is no transaction for free orders.
This caused them to stay in draft until manually cancelled.
[FIX] website_sale: avoid subscribing the website user (Public) to all shop orders

Especially as this user does not have a valid email, which
could prevent notifications to reach other followers.
[FIX] website: 'Display Editor Bar on Website' group stopped working at commit a2ef044c477

The Edit button never appeared anymore for these users.
The idea was that they should see an edit button with
limited editing capabilities depending on their other
access rights.
For example, someone with only Sales Manager access and
'Display Editor Bar on Website'
would be able to edit online quotes from the website_quote
module, but not change the actual website pages or menus,
for instance.
Merge branch '8.0' of https://github.com/odoo/odoo into 8.0-linux64