erp5_oauth_google_login: Set access_type as offline to be possible refresh token in background and automatically

access_type as offline indicates whether your application can refresh access tokens when the user is not present at the browser.

This value instructs the Google authorization server to return a refresh token and an access token the first time that your application exchanges an authorization code for tokens state.

Also the code was simplied to use oauth2client rather than http requests directly use persistent cache instead of ram cache to lose token if we restart all nodes