Test invoicing transaction transitions

I implement test cases for transitions of one type of invoicing
transaction to another one, e. g. quotes to sales orders or invoices to
credit memos.

Along this, I fix some bugs:

- do not copy carrier in transition because the carrier of the new
  invoicing transaction may be different from the one in the old
  invoicing transaction and the stage of the new invoicing transaction
  is always "created"
- when setting the date of a date selector input programmatically the
  underlying hidden input field was not updated

Furthermore, I implement methods to check input fields for the current
date and implement the forgotten test of the action bar in quotes and
sales orders.