Bug 24300: Add payout amount to boraccount page

Bug 24300: Add payout amount to boraccount page

Test plan
1/ Add some debts and credits to a patrons account, resulting in an
overall credit
2/ Note the appearance of a 'Payout amount' button next to the total due
line.
3/ Try paying out an amount with the button
4/ Signoff

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>