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/api.dart

@@ -452,6 +452,10 @@ class InvenTreeAPI {
     _connecting = false;
     _token = "";
     profile = null;
+
+    // Clear received settings
+    _globalSettings.clear();
+    _userSettings.clear();
   }
 
   Future<bool> connectToServer() async {
@@ -488,7 +492,9 @@ class InvenTreeAPI {
     return _connected;
   }
 
-
+  /*
+   * Request the user roles (permissions) from the InvenTree server
+   */
   Future<void> getUserRoles() async {
 
     roles.clear();
@@ -1143,4 +1149,32 @@ class InvenTreeAPI {
       cacheManager: manager,
     );
   }
+
+  bool get supportsSettings => isConnected() && apiVersion >= 45;
+
+  // Keep a record of which settings we have received from the server
+  Map<String, InvenTreeGlobalSetting> _globalSettings = {};
+  Map<String, InvenTreeUserSetting> _userSettings = {};
+
+  Future<String> getGlobalSetting(String key) async {
+
+    if (!supportsSettings) return "";
+
+    InvenTreeGlobalSetting? setting = _globalSettings[key];
+
+    if ((setting != null) && setting.reloadedWithin(Duration(minutes: 5))) {
+      return setting.value;
+    }
+
+    final response = await InvenTreeGlobalSetting().getModel(key);
+
+    if (response is InvenTreeGlobalSetting) {
+      response.lastReload = DateTime.now();
+      _globalSettings[key] = response;
+      return response.value;
+    } else {
+      return "";
+    }
+  }
+
 }

lib/inventree/model.dart

@@ -47,6 +47,14 @@ class InvenTreeModel {
   // Update whenever the model is loaded from the server
   DateTime? lastReload;
 
+  bool reloadedWithin(Duration d) {
+    if (lastReload == null) {
+      return false;
+    } else {
+      return lastReload!.add(d).isAfter(DateTime.now());
+    }
+  }
+
   // Override the endpoint URL for each subclass
   String get URL => "";
 
@@ -320,7 +328,7 @@ class InvenTreeModel {
   }
 
   // Return the detail view for the associated pk
-  Future<InvenTreeModel?> get(int pk, {Map<String, String> filters = const {}}) async {
+  Future<InvenTreeModel?> getModel(String pk, {Map<String, String> filters = const {}}) async {
 
     var url = path.join(URL, pk.toString());
 
@@ -367,6 +375,10 @@ class InvenTreeModel {
     return createFromJson(response.asMap());
   }
 
+  Future<InvenTreeModel?> get(int pk, {Map<String, String> filters = const {}}) async {
+    return getModel(pk.toString(), filters: filters);
+  }
+
   Future<InvenTreeModel?> create(Map<String, dynamic> data) async {
 
     if (data.containsKey("pk")) {

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,