title: Add shared row headers in matplotlib
body: <p>I haven't been able to find a way to add a shared row header across multiple subplots, as in the figure below. I don't want to use the xlabel of any plot, both because I need the label and because they don't align in the center of the row. I'd appreciate any suggestions.</p>
  
  <p><img src="https://i.stack.imgur.com/GGRhe.png" alt="Grid-Layout"></p>