Added updateOrders() to RetailSystemView interface
Added updateOrders() method implementation
Added unimplemented methd to RetailSystemBasicView
Added some methods to OrderPanel

updateProductList(products), updateOrderList(orders),
updateSupplierList(suppliers), and addListener(RetailViewListener)
Merge branch 'master' of https://github.com/d14123081/team4
Added some more comments to OrderPanel