Bug 19036: (QA follow-up) Add credit_number handling to POS

Bug 19036: (QA follow-up) Add credit_number handling to POS

This patch adds the display of 'credit_number' as a replacement for the
internal 'accountlines_id' as the transaction identifier on the
register summary page when using cash registers.

Test plan
1/ Enable 'UseCashRegisters'
2/ Enable 'EnablePointOfSale'
3/ Enable at least one 'Debit type' to allow 'sale'
4/ Add at least one 'Cash register'
5/ Enable 'AutoCreditNumber'
6/ 'Enable automatic generation of credit number' for the 'Purchase'
credit type
7/ Pay for an item via the Point of Sale page
8/ Navigate to the 'register' page to display the purchase details
9/ Confirm that the 'Transaction' is listed with a number of the form
specified in the 'AutoCreditNumber' preference
10/ Refund an item from this screen
11/ Note that the 'accountlines_id' is used for this refund as we did
not specify the 'Refund' credit type to use the 'AutoCreditNumber'
system
12/ Signoff

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>