Hiding plotting cells

[bsipocz]

@zzygKimmy pointed out that we have quite verbose plotting scripts that doesn't bring too much to the table for the flow of the notebooks. It would be very nice to be able to hide those cells, like one could do it in colab.

This issue is to find ways that work for ordinary notebooks, too.

[jakevdp]

In http://github.com/jakevdp/PythonDataScienceHandbook, I did this by putting those scripts in external .py files which save a static PNG, which the notebooks load. That's not a very satisfying solution, but it works well enough.

[bsipocz]

Thank you.
I hoped to find a notebook extension that would behave like colab, but falling back to .py files would also make sense, at least for the plots that we show for the background concepts rather than as a science case.