Remove requirement for both a Cost Centre and Department

Currently fee billing is capable of processing charges against nominal accounts with no cost centre or department, or those with both a cost centre and department only, but not with only one. For iFinance users, this means you have to have BI codes set up as 'CC-DEP' format, with double barrel BI codes. As a single school, our BI codes are not set up like this but as a single 'DEP' department code and as this is not an iFinance requirement, it should not really be a fee billing requirement.