Function add_google_mail 

pub(crate) fn add_google_mail(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    address: String,
    client_id: String,
    client_secret: String,
    again: Option<String>,
)

Adds an address’s Google mail, signed in on Google’s page, or signs its account in again (again: its id). Google’s page opens in the browser; the account’s server is tried with the access given before anything is kept. On a thread; the form says how it went.