Add configuration option to set the default quantity to zero rather than balance outstanding
17/11/14 Exson: Fixed InvoiceQuantityDefault parameters failed to save in SystemParameters.php. Reported by Ricard.
Check that all the general ledger transactuions balance
Location table sortable
14/11/14 Exson: Fixed the foreign key constrained failure bug in Z_DeleteCreditNote.php
Various bug fixes on leeway calculation