Examples: for relations demo add icons to buttons

Author: greenrobot-team

objectbox/example/flutter/objectbox_demo_relations/lib/main.dart

@@ -60,6 +60,7 @@ class _MyHomePageState extends State<MyHomePage> {
         floatingActionButton: FloatingActionButton.extended(
           key: const Key('add'),
           label: const Text('Add Task'),
+          icon: const Icon(Icons.add),
           heroTag: null,
           onPressed: () {
             Navigator.of(context).push(

objectbox/example/flutter/objectbox_demo_relations/lib/tag_elements.dart

@@ -27,6 +27,7 @@ class _NewTagState extends State<NewTag> {
   Widget build(BuildContext context) {
     return FloatingActionButton.extended(
       label: const Text('New Tag'),
+      icon: const Icon(Icons.add),
       heroTag: null,
       onPressed: () async {
         final dialog = await showDialog(