add 404 rule in admin

templates/admin/default/404.html

@@ -0,0 +1,14 @@
+{$page_title={intl l='Thelia'}}
+{include file='includes/header.inc.html'}
+
+    <div class="brandbar container">
+        <a class="brand" href="index.php">{images file='assets/img/logo-thelia-34px.png'}<img src="{$asset_url}" alt="{intl l='Thelia, solution e-commerce libre'}" />{/images}</a>
+    </div>
+
+    <div id="wrapper" class="container">
+        <h1>Oops! An Error Occurred</h1>
+        <h2>The server returned a "404 Not Found".</h2>
+    </div>
+
+
+{include file='includes/footer.inc.html'}