Function add_google_account 

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

Adds a Google account, or signs one in again (again: its id): Google’s page opens in your browser, Sioul waits for its answer here (Cancel stops the wait), finds the calendars and contacts, and syncs them. On a thread.