[ADD] website_sale: checkout process

Change checkout process.

- Billing address is always the connected partner_id or neww partner_id.
- Shipping address is contact of current commercial_partner_id
- New checkout design for address selection
- Add delete a line in my cart
- Fix input quantity size
- Refactor/Reindent xml template from website_sale
- Improve the modularity for checkout (preprocess, posprocess, required fields, ...)
- Allow to use form builder in extra step for OEE (No edit mode)
- Add route to have states according country selected (need to be overridable for website_sale_delivery)
- ...