title: Outline plot area in plotly in Python
body: <p>I've made a figure in plotly, e.g.:</p>
  
  <pre><code>import plotly.plotly as py
  import plotly.graph_objs as go
  
  trace1 = go.Scatter(
      x=[1, 2, 3, 4, 5, 6, 7],
      y=[7, 6, 5, 4, 3, 2, 1]
  )
  trace2 = go.Scatter(
      x=[1, 2, 3, 4, 5, 6, 7, 8],
      y=[1, 2, 3, 4, 5, 6, 7, 8]
  )
  data = [trace1, trace2]
  layout = dict(xaxis = dict(title = 'T (K)', showgrid=False, ticks='inside'),
                  yaxis = dict(title = 'normalized intensity', showgrid=False, ticks='inside'),
                  font=dict(size=18),
                  )
  fig = go.Figure(data=data, layout=layout)
  py.iplot(fig, auto_open=True, filename='test_fig.png')
  py.image.save_as(fig, filename='test_fig.png')
  </code></pre>
  
  <p>and the figure looks like:</p>
  
  <p><a href="https://i.stack.imgur.com/K3iIs.png" rel="noreferrer"><img src="https://i.stack.imgur.com/K3iIs.png" alt="test figure"></a></p>
  
  <p>I'd like an outline of the plot area like so:</p>
  
  <p><a href="https://i.stack.imgur.com/jq2JD.png" rel="noreferrer"><img src="https://i.stack.imgur.com/jq2JD.png" alt="outlined fig"></a></p>
  
  <p>but I am unable to figure it out from the plot.ly docs so far.  Is this possible?</p>