Adds code to requeest global setting from server

- Settings are individually cached for 5 minutes
- For now, use it for the purchase order reference prefix

lib/widget/paginator.dart

@@ -44,7 +44,6 @@ class PaginatedSearchState<T extends StatefulWidget> extends State<T> {
 
   Future<InvenTreePageResponse?> requestPage(int limit, int offset, Map<String, String> params) async {
 
-    print("Blank request page");
     // Default implementation returns null - must be overridden
     return null;
   }

lib/widget/purchase_order_detail.dart

@@ -37,6 +37,8 @@ class _PurchaseOrderDetailState extends RefreshableState<PurchaseOrderDetailWidg
 
   int completedLines = 0;
 
+  String _poPrefix = "";
+
   @override
   String getAppBarTitle(BuildContext context) => L10().purchaseOrder;
 
@@ -61,6 +63,9 @@ class _PurchaseOrderDetailState extends RefreshableState<PurchaseOrderDetailWidg
 
   @override
   Future<void> request(BuildContext context) async {
+
+    _poPrefix = await InvenTreeAPI().getGlobalSetting("PURCHASEORDER_REFERENCE_PREFIX");
+
     await order.reload();
 
     lines = await order.getLineItems();
@@ -72,7 +77,6 @@ class _PurchaseOrderDetailState extends RefreshableState<PurchaseOrderDetailWidg
         completedLines += 1;
       }
     }
-
   }
 
   Future <void> editOrder(BuildContext context) async {
@@ -93,7 +97,7 @@ class _PurchaseOrderDetailState extends RefreshableState<PurchaseOrderDetailWidg
 
     return Card(
         child: ListTile(
-          title: Text(order.reference),
+          title: Text("${_poPrefix}${order.reference}"),
           subtitle: Text(order.description),
           leading: supplier == null ? null : InvenTreeAPI().getImage(supplier.thumbnail, width: 40, height: 40),
         )

lib/widget/purchase_order_list.dart

@@ -55,9 +55,14 @@ class _PaginatedPurchaseOrderListState extends PaginatedSearchState<PaginatedPur
 
   _PaginatedPurchaseOrderListState(Map<String, String> filters) : super(filters);
 
+  // Purchase order prefix
+  String _poPrefix = "";
+
   @override
   Future<InvenTreePageResponse?> requestPage(int limit, int offset, Map<String, String> params) async {
 
+    _poPrefix = await InvenTreeAPI().getGlobalSetting("PURCHASEORDER_REFERENCE_PREFIX");
+
     params["outstanding"] = "true";
 
     final page = await InvenTreePurchaseOrder().listPaginated(limit, offset, filters: params);
@@ -72,9 +77,9 @@ class _PaginatedPurchaseOrderListState extends PaginatedSearchState<PaginatedPur
     InvenTreePurchaseOrder order = model as InvenTreePurchaseOrder;
 
     InvenTreeCompany? supplier = order.supplier;
-
+    
     return ListTile(
-      title: Text(order.reference),
+      title: Text("${_poPrefix}${order.reference}"),
       subtitle: Text(order.description),
       leading: supplier == null ? null : InvenTreeAPI().getImage(
         supplier.thumbnail,