title: PyQt5: gridlayout spacing issue
body: <p>I am a newbie in PyQt5. I'm trying to create a cell grid with a button at the bottom:</p>
  
  <pre><code> g = QGridLayout(window)     
   for i in range(N):
      for j in range(N):
          b = QPushButton()
          g.addWidget(b, i, j, 1, 1)
   g.addWidget(QPushButton("Last move"), N+4, N//2)
  </code></pre>
  
  <p>And this is what I get:</p>
  
  <p><img src="https://i.stack.imgur.com/CWe0K.png" alt="screenshot"></p>
  
  <p>As you see, the button spoils everything. How to can I get rid of the space between the cells?</p>