title: QDockWidget -- keep widgets as close as possible when resizing window
body: <p>I have a QDockWidget containing several QGroupBoxes. (The content of the QGroupBoxes is shown/hidden upon mousePressEvent.) I'm looking for a way to keep the QGroupBoxes positioned as tightly together as possible, preferably at the top of the DockWidget. It should look something like this: </p>
  
  <p><img src="https://dl.dropboxusercontent.com/u/4328598/desired_result.png" alt="desired result"></p>
  
  <p>However, when increasing the size of the DockWidget, the GroupBoxes drift apart:</p>
  
  <p><img src="https://dl.dropboxusercontent.com/u/4328598/drifting_apart.png" alt="current result"></p>
  
  <p>...which is very convenient in most cases, I know. But is there a way to override this behavior and get a nice, expandable, list-like grouping of Widgets?</p>
  
  <p>The DockWidget contains a QGroupBox; the QGroupBoxes 'Foo', 'Bar' and 'Baz' are added to that box's QVBoxLayout.</p>