message: Don't store any cookies with OAuth (third party)
  It was impossible to change your mind about the google account to use after logging in once.
diff: #include <QDebug>
  #include <QWebEngineView>
  +#include <QWebEngineProfile>
  +#include <QWebEngineCookieStore>
  LoginDialog::LoginDialog(QWidget *parent) :
  QDialog(parent),
  ui(new Ui::LoginDialog)
  {
  ui->setupUi(this);
  + ui->webView->page()->profile()->cookieStore()->deleteAllCookies();
  + ui->webView->page()->profile()->setPersistentCookiesPolicy(QWebEngineProfile::NoPersistentCookies);
  connect(ui->webView, SIGNAL(urlChanged(QUrl)), this, SLOT(urlChanged(QUrl)));
  }
  @@ -46,5 +50,6 @@ QString LoginDialog::accessToken()
  void LoginDialog::setLoginUrl(const QString& url)
  {
  + ui->webView->page()->profile()->cookieStore()->deleteAllCookies();
  ui->webView->setUrl(url);
  }
  