Add Return handler and plug it in the plugin

classes/Activitypub_error.php

@@ -0,0 +1,43 @@
+<?php
+/**
+ * GNU social - a federating social network
+ *
+ * Todo: Description
+ *
+ * PHP version 5
+ *
+ * LICENCE: This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @category  Plugin
+ * @package   GNUsocial
+ * @author    Diogo Cordeiro <diogo@fc.up.pt>
+ * @author    Daniel Supernault <danielsupernault@gmail.com>
+ * @copyright 2015 Free Software Foundaction, Inc.
+ * @license   http://www.fsf.org/licensing/licenses/agpl-3.0.html GNU Affero General Public License version 3.0
+ * @link      https://gnu.io/social
+ */
+
+if (!defined('GNUSOCIAL')) { exit(1); }
+
+class Activitypub_error extends Managed_DataObject
+{
+  public static function errorMessageToObject($m)
+  {
+    $res = [
+      'error'=> $m
+    ];
+
+    return $res;
+  }
+}