PyPlot: fix label position and annotate color bar

[pjaap]

This PR does the following in gridplot with PyPlot

• display the correct number of boundary regions (needs Use concrete number of grid regions GridVisualizeTools.jl#9)
• labels the color bar
• use correct position of the ticks in the color bar
• annotates the color bar with "boundary regions"

Before:

After:

[j-fu]

Cool. But the idea is that cell regions are in pastel colors and boundary regions in bright.
Also, not sure which are more important to have if there is only one colorbar possible. I think it's the boundary regions. Not sure if we should go down the rabbit hole and add more options...

[pjaap]

True, the colors are wrong. That is hopefully not so difficult to fix. And that thy the annotation "boundary regions" is so important :)

[pjaap]

Sigh. It does not seem as simple as it looks. The problem here is that originally, we create a tripcolorplot that shows the colored triangulation and then add a colorbar that describes the plot. However, we do not want to describe the plot, but only the boundary colors.

I uploaed a HACK!! where we simply use tripcolor twice to overwrite the plot with pastel colors but show the colorbar of the pastel colors. I am not an expert on PyPlot, to be honest :)

But the result is a desired:

@j-fu Do you know how to make this elegantly in the code?

[j-fu]

Not really. May be it works as well if you plot just one triangle for the first plot.
python plotting is relatively slow, and the slowdown from plotting twice possibly is nontrivial.

[pjaap]

Rebased.

I changed the dummy plot to plot only one triangle (I extract the first 3 coordinates). Results are as shown before.

[j-fu]

Well, it crashes for me. Can you try what I described:

https://wias-pdelib.github.io/GridVisualize.jl/stable/contributing/

on your computer ?

(it may make sense to check the pyplot case along with CairoMakie and PlutoVista in the CI).

[pjaap]

Thanks for the pointer, I didn't know that one. I'll add some code to the unit tests that catch the failure.