title: is it possible to return the edge/node info to python after rendering in bokeh?
body: <p>I have used this code to draw network diagram.
  so far, I have seen ways to change graph attributes when click or hover.
  but now I want to record object info when clicked
  for example: if I click on an edge, I want to return to python the edge details to do some processing.</p>
  
  <pre><code>import networkx as nx
  
  from bokeh.io import show, output_file
  from bokeh.models import Plot, Range1d, MultiLine, Circle, HoverTool, TapTool, BoxSelectTool
  from bokeh.models.graphs import from_networkx, NodesAndLinkedEdges, EdgesAndLinkedNodes
  from bokeh.palettes import Spectral4
  
  G=nx.karate_club_graph()
  
  plot = Plot(plot_width=400, plot_height=400,
              x_range=Range1d(-1.1,1.1), y_range=Range1d(-1.1,1.1))
  plot.title.text = "Graph Interaction Demonstration"
  
  plot.add_tools(HoverTool(tooltips=None), TapTool(), BoxSelectTool())
  
  graph_renderer = from_networkx(G, nx.circular_layout, scale=1, center=(0,0))
  
  graph_renderer.node_renderer.glyph = Circle(size=15, fill_color=Spectral4[0])
  graph_renderer.node_renderer.selection_glyph = Circle(size=15, fill_color=Spectral4[2])
  graph_renderer.node_renderer.hover_glyph = Circle(size=15, fill_color=Spectral4[1])
  
  graph_renderer.edge_renderer.glyph = MultiLine(line_color="#CCCCCC", line_alpha=0.8, line_width=5)
  graph_renderer.edge_renderer.selection_glyph = MultiLine(line_color=Spectral4[2], line_width=5)
  graph_renderer.edge_renderer.hover_glyph = MultiLine(line_color=Spectral4[1], line_width=5)
  
  graph_renderer.selection_policy = NodesAndLinkedEdges()
  graph_renderer.inspection_policy = EdgesAndLinkedNodes()
  
  plot.renderers.append(graph_renderer)
  
  output_file("interactive_graphs.html")
  show(plot)
  </code></pre>