title: One QAction checkable at time in QMenu
body: <p>I am trying to make my choices from QMenu to be checkable in a way that only one might be selected at time and first item is set checked by default (this works actually).</p>
  
  <p>Here is a snippet of my code:</p>
  
  <pre><code>paymentType = QMenu('Payment Type', self)
  paymentType.addAction(QAction('Cash', paymentType, checkable=True, checked = True))
  paymentType.addAction(QAction('Noncash Payment', paymentType, checkable=True))
  paymentType.addAction(QAction('Cash on Delivery', paymentType, checkable=True))
  paymentType.addAction(QAction('Bank Transfer', paymentType, checkable=True))
  menu.addMenu(paymentType)
  </code></pre>
  
  <p>Any suggestions? Thanks!</p>