Bokeh legends

[ahartikainen]

Add (interactivate) legend (intuitive interactivity)

https://docs.bokeh.org/en/1.4.0/docs/reference/models/annotations.html#bokeh.models.annotations.Legend

https://docs.bokeh.org/en/1.4.0/docs/user_guide/interaction/legends.html

[OriolAbril]

I'll reopen in hopes of reminding myself some day to try interactive legend in plot_trace