Split 'part' model into new file

lib/inventree/part.dart

@@ -0,0 +1,55 @@
+import 'package:InvenTree/api.dart';
+
+import 'model.dart';
+import 'dart:convert';
+
+import 'package:path/path.dart' as path;
+import 'package:http/http.dart' as http;
+
+class InvenTreePartCategory extends InvenTreeObject {
+  @override
+  String URL = "part/category/";
+
+  String get pathstring => jsondata['pathstring'] ?? '';
+
+  InvenTreePartCategory() : super();
+
+  InvenTreePartCategory.fromJson(Map<String, dynamic> json) : super.fromJson(json) {
+
+  }
+
+  @override
+  InvenTreeObject _createFromJson(Map<String, dynamic> json) {
+    var cat = InvenTreePartCategory.fromJson(json);
+
+    // TODO ?
+
+    return cat;
+  }
+}
+
+
+class InvenTreePart extends InvenTreeObject {
+
+  @override
+  String URL = "part/";
+
+  int get categoryId => jsondata['category'] as int ?? -1;
+
+  String get categoryName => jsondata['category__name'] ?? '';
+
+  InvenTreePart() : super();
+
+  InvenTreePart.fromJson(Map<String, dynamic> json) : super.fromJson(json) {
+    // TODO
+  }
+
+  @override
+  InvenTreeObject _createFromJson(Map<String, dynamic> json) {
+
+    var part = InvenTreePart.fromJson(json);
+
+    return part;
+
+  }
+}