Bug 28147: Pass itemnumber through to Account->pay

Bug 28147: Pass itemnumber through to Account->pay

Currently the itemnumber is not passed through when paying a single fine,
we should do that

To test:
1 - Create a manual debit and provide a barcode so the debit is linked to an item
2 - Go to the 'Make a payment' tab. Click the 'Writeoff' button on the individual line
3 - View the 'Transactions tab' The writeoff has no item details
4 - Apply patch
5 - Repeat 1 & 2
6 - View the transactions tab. The writeoff shows item details
7 - Confirm 'Writeoff amount' and 'Writeoff selected' still work and do not link to item

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>