(TODO: Re-assign when we agree on spec. Be sure to update unit-tests.)
HR-131 added the HRJobPay.pay_currency field. This means that stats of "Monthly Cost" and "Annual Cost" will include mixed currencies.
Proposal: If "Monthly Cost" or "Annual Cost" is included, then automatically add "Pay Currency" as a group-by field and display the column.
Fallback: Add an option to the UI which allows user to group-by/display the "Pay Currency" column.