Draft Invoice - Customer Tax

1) Ability to set a default customer tax, ie For customer Foo the default tax 5%. This will speed up the process of issuing an invoice wihout need to change the item tax for a specific client
2) A draft invoice or a Proformal Invoice without applying the invoice incremental value. This will help the user to issue a proformal/draft invoices and if the clients accepts to registererd it and obtain the incremential number.