8.0 new addons: sale_quotation_sourcing

`sale_quotation_sourcing` allows to invert the purchase sourcing logic in Odoo. In this mode, an RFQ is sent to to suppliers *before* the SO is confirmed (in order to get the best quote, and to ensure that the price communicated to the customer is computed based on that quote). When the SO is confirmed, a link can be made to the RFQ to use for sourcing the sale, and the procurement order will not create a new PO. 
@nbessi done