title: Best method for detecting input changes with QDataWidgetMapper
body: <p>I'm using QDataWidgetMapper for editing data-base.
  Does QDataWidgetMapper or any class (parent/mapped widgets/etc.) emit a signal, when any user-data in mapped widgets changes? At least, is it possible to check the changes by a method call manually?</p>
  
  <p>I want the user to approve changes before submit and to display an icon on the form if something has changed.</p>
  
  <p>It appears to me to be a very basic feature, but I can't find it.</p>
  
  <p>Should I really connect each mapped widget and check the changes for each widget individually? </p>