[securemail] Update Composer dependencies

- Update phpseclib/phpseclib to version 2.0.4
- Update singpolyma/openpgp-php to version 0.3.0

securemail/vendor/autoload.php

@@ -0,0 +1,7 @@
+<?php
+
+// autoload.php @generated by Composer
+
+require_once __DIR__ . '/composer/autoload_real.php';
+
+return ComposerAutoloaderInitSecuremailAddon::getLoader();