Update animation tutorial

[gregtucker]

The animation tutorial seems to be producing blank output in some cases. I recommend modifying it to use MPL's FuncAnimation, which I've had good luck with recently.

[nathanlyons]

#45 addresses the blank output when tutorials are run locally and improves the tutorial overall. They still do not show when on GitHub.

Have you used FuncAnimation with imshow_grid? In prior attempts, I found using imshow_grid with FuncAnimation is messy. For one, the imshow image and the colorbar have to be located using pyplot functions because imshow_grid does not return these. I would like to hear if you have used imshow_grid with FuncAnimation without many workarounds.

Aspects of animating imshow_grid in a Jupyter notebook are cumbersome. Some of this was circumvented in the tutorial by using longer than probably advisable code blocks.

[gregtucker]

@nathanlyons I have not tried FuncAnimation with imshow_grid, and did not realize there were issues with this.