Google Login follow the same implementation of ERP5 Login(subobject of Person) and with an action in preferences, the user can add Google Login to his person.

- A link was add to login page in ERP5 with Google Account and zocial.min.css is used to display it nicely

- logout was extended to remove cookie __ac_google_hash if authentication with Google account is enabled

- login_form is using ERP5Site_getAvailableOAuthLoginList to know if google login is supported or not. With this, we can extend to other oauth easily.

- ERP5ExternalOauth2ExtractionPlugin don't have the responsability of create user in extraction plugin. A more apporpriate place would be a dedicated "signup using oauth" page, relying on erp5_credential for the actual user creation.

- portal_oauth is used to store secret_key and client_id from Google

- enable PAS plugin through upgrader