Save php sessions in myaac dir

Instead of default PHP location
This fixes problem with permissions

common.php

@@ -24,7 +24,6 @@
  * @link      https://my-aac.org
  */
 if (version_compare(phpversion(), '5.6', '<')) die('PHP version 5.6 or higher is required.');
-session_start();
 
 define('MYAAC', true);
 define('MYAAC_VERSION', '0.8.6');
@@ -86,6 +85,9 @@ define('TFS_03', 4);
 define('TFS_FIRST', TFS_02);
 define('TFS_LAST', TFS_03);
 
+session_save_path(SYSTEM . 'php_sessions');
+session_start();
+
 // basedir
 $basedir = '';
 $tmp = explode('/', $_SERVER['SCRIPT_NAME']);