title: Changing matplotlib window title is throwing strange error
body: <p>I'm using python 3.6 in Jupyter lab on a linux mint machine to run this snippet of code</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  fig = plt.figure()
  man = plt.get_current_fig_manager()
  man.window.setWindowTitle("New Title")
  </code></pre>
  
  <p>..it returns the following error message:</p>
  
  <pre><code>AttributeError: 'FigureManagerBase' object has no attribute 'window'
  </code></pre>
  
  <p>I have checked the GUI backends. All are available and all of them return this error even if I force the backend using ...</p>
  
  <pre><code>import matplotlib
  matplotlib.use(&lt;gui&gt;,warn=False, force=True)
  </code></pre>
  
  <p>...before importing pyplot. The code has been working OK in Spyder but I've had to move to Jupyter. The matplotlib docs say that FigureManagerBase attributes include 'window'. I'm stumped</p>