title: how to set QLineEdit to readonly if the data mapped by QDataWidgetMapper is readonly?
body: <p>I have a tree model and use <code>QDataWidgetMapper</code> to map the model data to some widgets.</p>
  
  <p>In the model, some of the data are flagged as read-only, so, what I would like to do is to let the mapped widget, say, a <code>QLineEdit</code>, be able to act upon this flag and set itself to readonly when the model data it points to is readonly.</p>
  
  <p>Any help is appreciated!</p>