Improve splitting items in billing
Billing in Mews only enables properties to split items between multiple guests but it doesn't allow properties to split 1 item beteen multiple guests.
If 2 guests want to split the cost of e.g. 1 night, Mews doesn't support issuing 2 invoices to both guests for this night.
Improve splitting items so that each guest can receive a an invoice if they want to split e.g. 1 night between multiple guests.