title: How to subclass QMessageBox and add a progress bar in PySide
body: <p>I'm rather new to PySide, and Qt in general. I want to add a QProgressBar to a QMessageBox where the buttons would usually be. I'm hoping that there's some way to subclass QMessageBox and change it's layout, but I've never done a Qt layout in code, I've done everything with Qt Designer and pyside-uic.</p>
  
  <p>I've created a concept in Qt Designer, I'd like to have something similar to this done by sub-classing QMessageBox. I've looked at QProgressDialog, but it's too inflexible. I'd like to be able to use the QMessageBox Icon enum for the icon. </p>
  
  <p><img src="https://i.stack.imgur.com/QViBY.png" alt="Concept"></p>