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>

sources/Core/Authentication/Client/OAuth/IOAuthClientProvider.php

@@ -0,0 +1,5 @@
+<?php
+namespace Combodo\iTop\Core\Authentication\Client\OAuth;
+
+interface IOAuthClientProvider{
+}