Bug 15896 - Use Koha::Account::pay internally for makepayment

Bug 15896 - Use Koha::Account::pay internally for makepayment

This is the second patch in a series to unify all payment functions into
a single mathod

Test Plan:
1) Apply this patch
2) prove t/db_dependent/Accounts.t
3) Test fine payment via the "Pay" button

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Followed test plan, works as expected.
Signed-off-by: Marc Veron <veron@veron.ch>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>