Include box_zoom tool in plot tool bars

[nmgeek]

Maybe it's just me but I cannot get to the desired frame of a zoomed in plot without a box zoom tool. With the plot navigation tools that GridPath displays, I have to go back and forth between the pan tool and the zoom_in tool several times to get there.

If you simply drop the tool parameter to the bokeh figure function call, then the selection of tools includes the box_zoom tool which makes it easier to zoom in.

https://github.com/blue-marble/gridpath/blob/570f47560bd38e1ea8700a5b9da9c8f489d43d84/viz/energy_target_plot.py#L154