title: pyqt designer and layout for central widget
body: <p>I started new clear Main Window project,</p>
  
  <p>There are 4 Objects: MainWindow, centralWidget, menubar, and statusbar.</p>
  
  <p>I need to set default layout inside the window, so probably for centralWidget.</p>
  
  <p>But I didnt found way how to do it.
  I can get LayoutWidget with some particular size into centralWidget.</p>
  
  <p>But I want to set layout for the whole centralWidget.</p>