fixed disappearing lists on edit

lib/api/list_implementation.dart

@@ -13,6 +13,7 @@ class ListAPIService extends APIService implements ListService {
 
   @override
   Future<TaskList> create(namespaceId, TaskList tl) {
+    tl.namespaceId = namespaceId;
     return client
         .put('/namespaces/$namespaceId/lists', body: tl.toJSON())
         .then((response) => TaskList.fromJson(response.body));

lib/models/list.dart

@@ -4,7 +4,8 @@ import 'package:vikunja_app/models/user.dart';
 
 class TaskList {
   final int id;
-  final String title, description;
+  int namespaceId;
+  String title, description;
   final User owner;
   final DateTime created, updated;
   List<Task> tasks;
@@ -12,13 +13,14 @@ class TaskList {
 
   TaskList(
       {@required this.id,
-      @required this.title,
       this.description,
+      @required this.title,
       this.owner,
       this.created,
       this.updated,
       this.tasks,
-      this.isFavorite});
+      this.isFavorite,
+      this.namespaceId});
 
   TaskList.fromJson(Map<String, dynamic> json)
       : id = json['id'],
@@ -28,6 +30,7 @@ class TaskList {
         updated = DateTime.parse(json['updated']),
         created = DateTime.parse(json['created']),
         isFavorite = json['is_favorite'],
+        namespaceId = json['namespace_id'],
         tasks = (json['tasks'] == null ? [] : json['tasks'] as List<dynamic>)
             ?.map((taskJson) => Task.fromJson(taskJson))
             ?.toList();
@@ -40,6 +43,7 @@ class TaskList {
       "owner": this.owner?.toJSON(),
       "created": this.created?.toIso8601String(),
       "updated": this.updated?.toIso8601String(),
+      "namespace_id": this.namespaceId
     };
   }
 }

lib/pages/list/list.dart

@@ -59,11 +59,7 @@ class _ListPageState extends State<ListPage> {
 
   @override
   void initState() {
-    _list = TaskList(
-      id: widget.taskList.id,
-      title: widget.taskList.title,
-      tasks: [],
-    );
+    _list = widget.taskList;
     _keyboardController.onChange.listen((visible) {
       if (!visible && mounted) FocusScope.of(context).unfocus();
     });

lib/pages/list/list_edit.dart

@@ -136,10 +136,9 @@ class _ListEditPageState extends State<ListEditPage> {
     setState(() => _loading = true);
     // FIXME: is there a way we can update the list without creating a new list object?
     //  aka updating the existing list we got from context (setters?)
-    TaskList updatedList =
-        TaskList(id: widget.list.id, title: _title, description: _description);
-
-    VikunjaGlobal.of(context).listService.update(updatedList).then((_) {
+    widget.list.title = _title;
+    widget.list.description = _description;
+    VikunjaGlobal.of(context).listService.update(widget.list).then((_) {
       setState(() => _loading = false);
       ScaffoldMessenger.of(context).showSnackBar(SnackBar(
         content: Text('The list was updated successfully!'),