title: Qt Layout, resize to minimum after widget size changes
body: <p>Basically I've got a <code>QGridLayout</code> with a few widgets in it. The important ones are 2 labels, which I use for drawing images to the screen. Well, if the user wants, he can change the resolution of the incoming images, thus, forcing the Labels to resize. </p>
  
  <p>Let's assume the initial size of the label is <code>320x240</code>. The user changes the VideoMode to <code>640x480</code>, the label and the entire GUI resizes perfectly. But when the user switches back to <code>320x240</code>, the label shrinks, but the Layout/Window does NOT.</p>
  
  <p>I've played around with <code>sizePolicies</code> and <code>sizeHints</code>, and <code>resize(0,0)</code>, but nothing did the trick. Could somebody help me with this?</p>
  
  <p>Here some screenshots to clarify the problem:</p>
  
  <p><img src="https://i.stack.imgur.com/uRart.png" alt="Here, everything is okay">
  <img src="https://i.stack.imgur.com/UpbYw.png" alt="still, 640 x 480 resizes perfectly">
  <img src="https://i.stack.imgur.com/d0RiY.png" alt="but here, the layout is too big."></p>