Ajout de la page listant les emails des utilisateurs

backend/views/user/index.php

 ?>
 <div class="user-index">
 
-    <h1><?= Html::encode($this->title) ?></h1>
+    <h1><?= Html::encode($this->title) ?> <?= Html::a('<span class="glyphicon glyphicon-envelope"></span> Liste des emails', ['mail'], ['class' => 'btn btn-default']) ?></h1>
 
     <?= GridView::widget([
         'dataProvider' => $dataProvider,

backend/views/user/liste_mails.php

  * and open the template in the editor.
  */
 
-$this->title = 'Liste des emails utilisateurs';
+use yii\helpers\Html ;
+
+$this->title = 'Liste des emails';
+$this->params['breadcrumbs'][] = ['label' => 'Utilisateurs', 
+    'url' => ['user/index']] ;
+$this->params['breadcrumbs'][] = $this->title;
 
 ?>