Feature/merge 3 0 develop (#298)

* merging 3.0 into develop

* N°5102 - Allow to send emails (eg. notifications) using GSuite SMTP and OAuth
* migration to iTop 3.1

Co-authored-by: Eric Espie <eric.espie@combodo.com>

lib/guzzlehttp/guzzle/src/functions_include.php

@@ -0,0 +1,6 @@
+<?php
+
+// Don't redefine the functions if included multiple times.
+if (!function_exists('GuzzleHttp\uri_template')) {
+    require __DIR__ . '/functions.php';
+}