THIS FUNCTION IS CURRENTLY IMPLEMENTED ONLY FOR THE "app" NAMESPACE - NOT FOR "api"
This function will only add line to the cart - not to the "order center"
LeadingLine is optional - it should be used for "bonus items" to assign an item to it's "parent" item.
pepperi.app.transactions.addLines({ transaction:{UUID:"11cda91f-df09-4d3c-826d-184e5f394d06"},lines:[{ item:{ExternalID:"MCR00101BLUEL"},lineData:{ UnitsQuantity:5 } }],leadingLine:{UUID:"11cda91f-df09-4d3c-826d-184e5f394d0d"}})