title: Set QGroupBox title font size with style sheets
body: <p>I would like to be able to set the font size of the title of a QGroupBox using style sheets.  I can't seem to figure it out.</p>
  
  <p>Based on what I've read <a href="http://qt-project.org/doc/qt-4.7/stylesheet-examples.html#id-bfd71794-8c48-4cff-a7bf-d5fe48e62558" rel="noreferrer">here</a>, I've come up with the following code.  Unfortunately, it doesn't quite work.</p>
  
  <pre><code>groupbox-&gt;setStyleSheet(style)
  </code></pre>
  
  <p>Where <code>style</code> is:</p>
  
  <pre><code>QGroupBox::title
  {
      subcontrol-origin: margin;
      subcontrol-position: top left;
      padding: 5 5px;
      font-size: 18px;
      font-weight: bold;
  }
  </code></pre>
  
  <p>All of those style elements seem to be honored except <code>font-size</code> and <code>font-weight</code>.  According to the <a href="http://qt-project.org/doc/qt-5.0/qtwidgets/stylesheet-reference.html" rel="noreferrer">Qt Style Sheets Reference</a>, the font "property is supported by all widgets that respect the QWidget::font."  Is this not the case for a QGroupBox's title?</p>