Add Google OpenId support

Hello Jérôme,

We actually have a project using Google OpenId authentication. As we plan to provide other authentication methods, we recently made the swich to pac4j.
In order to avoid user migrations, we worked on adding the support for Google OpenId authentication.

However, the test for it need to be completed because we were unable to retrieve some of the needed information (because of Google's security policy).
See TODOs.

Thanks for your feedback.

--
Stéphane