Added Feature in Formulas - Expenses and Extras

Hi! We need to have a feature that separates expenses and extras.

Here's why. 

Many property managers (like myself) when invoicing clients follow this method: 

Owner Payout-Cleaning Fees (expenses)*PM Commission+Extras

Extras in this case would be expenses that need to be paid back to me as the property manager. We don't charge a commission on re-imbursements. 

Right now you can't separate expenses and extras.