[Oembed] Refactoring and some improvements (namely documentation)

Imported some changes from postActiv

plugins/Oembed/scripts/poll_oembed.php

@@ -1,7 +1,33 @@
 #!/usr/bin/env php
 <?php
+// This file is part of GNU social - https://www.gnu.org/software/social
+//
+// GNU social 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.
+//
+// GNU social 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 GNU social.  If not, see <http://www.gnu.org/licenses/>.
 
-define('INSTALLDIR', realpath(dirname(__FILE__) . '/../../..'));
+/**
+ * OembedPlugin implementation for GNU social
+ *
+ * @package   GNUsocial
+ * @author    Mikael Nordfeldth
+ * @author    Diogo Cordeiro <diogo@fc.up.pt>
+ * @copyright 2019 Free Software Foundation, Inc http://www.fsf.org
+ * @license   https://www.gnu.org/licenses/agpl.html GNU AGPL v3 or later
+ */
+
+defined('GNUSOCIAL') || die();
+
+define('INSTALLDIR', realpath(__DIR__ . '/../../..'));
 
 $shortoptions = 'u:';
 $longoptions = array('url=');