title: Add a vertical label to matplotlib colormap legend
body: <p>This code enables me to plot a colormap of a "3d" array [X,Y,Z] (they are 3 simple np.array of elements). But I can't succeed in adding a vertical written label at the right of the colorbar legend. </p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  fig = plt.figure("Color MAP 2D+")
  
  contour = plt.tricontourf(X, Y, Z, 100, cmap="bwr")
  
  plt.xlabel("X")
  plt.ylabel("Y")
  plt.title("Color MAP 2D+")
  
  #Legend
  def fmt(x, pos):
      a, b = '{:.2e}'.format(x).split('e')
      b = int(b)
      return r'${} \times 10^{{{}}}$'.format(a, b)
  import matplotlib.ticker as ticker
  plt.colorbar(contour, format=ticker.FuncFormatter(fmt))
  
  plt.show()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/QwjmO.png" rel="noreferrer"><img src="https://i.stack.imgur.com/QwjmO.png" alt="enter image description here"></a></p>
  
  <p>It's anoying to not get an easy answer from google... can someone help me ?</p>