Update interactivity figure for bokeh and matplotlib changes

[jbednar]

The figure at https://datashader.org/assets/images/ds_hv_bokeh2.png used on https://datashader.org/getting_started/Interactivity.html is out of date:

1. It shows that a developer could use Datashader + Bokeh directly, which used to be true, but has not been supported for many years now (since long before removing bokeh_ext.py).
2. It doesn't show that Datashader + Matplotlib is supported, both directly and via HoloViews.

There may be other updates needed as well. I've attached my original GIMP (XCF) source files for this image, in two different versions (not sure which is better).