Use origin instead of description when paying invoice

The payment move on an invoice must be linked to the invoice with the origin
field and let the description as free text for the user. As there is only one
description for the move, it should be stored on the move instead of the line.

issue7702
review46641002

invoice.py

@@ -1192,8 +1192,8 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
         Line = pool.get('account.move.line')
         Period = pool.get('account.period')
 
-        line1 = Line(description=description, account=self.account)
-        line2 = Line(description=description)
+        line1 = Line(account=self.account)
+        line2 = Line()
         lines = [line1, line2]
 
         if amount >= 0:
@@ -1226,6 +1226,7 @@ class Invoice(Workflow, ModelSQL, ModelView, TaxableMixin):
 
         move = Move(
             journal=payment_method.journal, period=period_id, date=date,
+            origin=self, description=description,
             company=self.company, lines=lines)
         move.save()
         Move.post([move])
@@ -2603,7 +2604,6 @@ class PayInvoice(Wizard):
         default['currency_digits'] = invoice.currency.digits
         default['amount'] = (invoice.amount_to_pay_today
             or invoice.amount_to_pay)
-        default['description'] = invoice.number
         default['invoice_account'] = invoice.account.id
         return default