update global melt cookbook

[jdannberg]

At the moment, this cookbook crashes on main (after a few time steps).
This fix is in response to https://community.geodynamics.org/t/problems-with-global-melt-cookbook/3043 and https://community.geodynamics.org/t/unable-to-reproduce-global-melt-cookbook-results-in-the-aspect-manual/3093.
As mentioned on the forum, I believe this is because of our changes to the artificial diffusion.

To make the cookbook work again, I

• increased the resolution
• refined the mesh near the top and bottom
• increased the temperature and age of the bottom boundary (we had more conduction before with the old artificial viscosity, so the plumes on the current main are thinner/colder than they used to be, and this makes them hotter again so that there actually is some melting)
• increased the end time

I updated the figure in the cookbook accordingly. I also updated the prm files in the doc folder, which are just copies of parts of the actual cookbooks. Those had gotten out of date as well, so the typo/documentation changes in those files are just because I copied over the actual cookbook prm files.

• I have followed the instructions for indenting my code.

[tjhei]

Very nice, thanks for fixing.