title: Set axes label in coordinate system of figure rather than axes
body: <p>I would like to use the coordinate system of the figure rather than the axis to set the coordinates of the axes label (or if this is not possible at least some absolute coordinate system).</p>
  
  <p>In other words I would like to the label at the same position for this two examples:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from pylab import axes
  
  plt.figure().show()
  ax = axes([.2, .1, .7, .8])
  ax.plot([1, 2], [1, 2])
  ax.set_ylabel('BlaBla')
  ax.yaxis.set_label_coords(-.1, .5)
  plt.draw()
  
  plt.figure().show()
  ax = axes([.2, .1, .4, .8])
  ax.plot([1, 2], [1, 2])
  ax.set_ylabel('BlaBla')
  ax.yaxis.set_label_coords(-.1, .5)
  
  plt.draw()
  plt.show()
  </code></pre>
  
  <p>Is this possible in matplotlib?</p>
  
  <p><img src="https://i.stack.imgur.com/gsn07.gif" alt="Illustrate difference"></p>