Label printing fix (#489)

* Add check for modern label printing interface

* Update getLabelTemplates

* Fix typo

* Refactor / simplify

* Revert parameter type

* Update version number and release notes

* Refactor label printing function

- Will require some cleanup in the future
- Still needs testing

* Fix for modern printing

* Typo fix

lib/inventree/model.dart

@@ -64,6 +64,9 @@ class InvenTreeModel {
   // Note: If the WEB_URL is the same (except for /api/) as URL then just leave blank
   String get WEB_URL => "";
 
+  // Return the "model type" of this model
+  String get MODEL_TYPE => "";
+
   // Helper function to set a value in the JSON data
   void setValue(String key, dynamic value) {
     jsondata[key] = value;

lib/inventree/part.dart

@@ -196,6 +196,9 @@ class InvenTreePart extends InvenTreeModel {
   @override
   String get URL => "part/";
 
+  @override
+  String get MODEL_TYPE => "part";
+
   @override
   List<String> get rolesRequired => ["part"];
 

lib/inventree/purchase_order.dart

@@ -20,6 +20,9 @@ class InvenTreePurchaseOrder extends InvenTreeOrder {
   @override
   String get URL => "order/po/";
 
+  @override
+  String get MODEL_TYPE => "purchaseorder";
+
   @override
   List<String> get rolesRequired => ["purchase_order"];
 

lib/inventree/sales_order.dart

@@ -23,6 +23,9 @@ class InvenTreeSalesOrder extends InvenTreeOrder {
   @override
   String get URL => "order/so/";
 
+  @override
+  String get MODEL_TYPE => "salesorder";
+
   @override
   List<String> get rolesRequired => ["sales_order"];
 

lib/inventree/stock.dart

@@ -142,6 +142,9 @@ class InvenTreeStockItem extends InvenTreeModel {
   @override
   String get URL => "stock/";
 
+  @override
+  String get MODEL_TYPE => "stockitem";
+
   @override
   List<String> get rolesRequired => ["stock"];
 
@@ -649,6 +652,9 @@ class InvenTreeStockLocation extends InvenTreeModel {
   @override
   String get URL => "stock/location/";
 
+  @override
+  String get MODEL_TYPE => "stocklocation";
+
   @override
   List<String> get rolesRequired => ["stock_location"];