title: Borderless window with Aero Snap too large in maximized state
body: <p>I am trying to make a borderless window in Qt5.6.0, with aero-snap functionality.
  Everything works, except when I maximize the window : it is too big.</p>
  
  <p>My screen resolution is <code>2560x1440</code>, so the window should be sized <code>2560x1400</code> (40 Pixels for the Taskbar), but in the <code>WM_SIZE</code> message, the new size is <code>2576x1416</code>.
  So the window is exactly 8 pixels too big in every direction.
  This also means that the window is not aligned in the top-left corner, it is exactly 8 pixels off-screen in both directions.</p>
  
  <p>I can't find a solution for this problem, everything I have tried doesn't work and causes bugs. </p>
  
  <p>The only thing that fixes this is to remove the <code>WS_CAPTION</code> and <code>WS_THICKFRAME</code> styles, but then I lose the areo snap functionality.</p>
  
  <p>I somehow have to tell Qt or DWM to make the window 16 pixels smaller and move it 8 pixels right, and bottom. Does anybody have an idea on how to do that?</p>