OpenBill A class represnting an open invoice which the user has to pay for a certain merchant.
new OpenBill( billId, billTypeName, dueDate, amount )
| Name | Type | Description |
| billId | The id of this invoice/bill | |
| billTypeName | The name of the bill type for this invoice | |
| dueDate | The due date of this bill | |
| amount | The amount due for this bill |