Structural categories (#220)

* Add support for editing "structural" tree field

- Requires API v83 or newer

* Update release notes

lib/inventree/stock.dart

@@ -652,13 +652,18 @@ class InvenTreeStockLocation extends InvenTreeModel {
 
   @override
   Map<String, dynamic> formFields() {
-    return {
+    Map<String, dynamic> fields = {
       "name": {},
       "description": {},
-      "parent": {
-
-      },
+      "parent": {},
+      "structural": {},
     };
+
+    if (!api.supportsStructuralCategories) {
+      fields.remove("structural");
+    }
+
+    return fields;
   }
 
   String get parentPathString {