Stock batch picking extended account sale type

This module extends the automatic invoicing of batch transfers so the decision can be driven by the sale order type instead of only by the customer.

• On the customer (res.partner), the existing "Auto invoice" setting gains a new choice, "By sale type". When a customer is set to this option, Odoo will only invoice a batch automatically if the sale order type used on the related sale order also has automatic invoicing enabled.
• On the sale order type (sale.order.type), a new checkbox "Batch picking auto invoice" is added to the form, next to the warehouse field. Tick it to say that batches coming from orders of this type should be invoiced automatically.
• The batch transfer (stock.picking.batch) logic that decides which pickings are eligible for invoicing is extended: a picking now also qualifies when the customer is set to "By sale type" and the sale order's type has the checkbox ticked.

In practice, a warehouse or accounting user configures the customer and the sale order type once, then simply validates batch transfers as Done; invoices are generated automatically for the matching pickings, without having to select them manually.