Features:
- Enhanced the full page invoice by allowing the "Avail Credit" value to hide if there is no balance. Also renamed to "Store Credit Bal".
- Fixed test print button for full page invoice. This is not supported so an extra check was added to inform the user properly.
- Fixed the followup (change due) screen to properly enable the open drawer button when applicable.
- Finalized cash drawer separation from the receipt printer options. These devices are now totally independent.