perhaps Include EU (big 4) and other EU regions

[knbknb]

I think it Would be useful to also have "EU-big-4" (DE, IT, FR, ESP) selectable in the Sidebar, at the top of the List of Checkboxes.

Perhaps also a few more, generalized by region:

• nordic countries
• Mediterreaean
• EU, Northwest (UK, BEL, NL, DE, Ö) .
• Eastern Europe

I know that their authorities are counting cases differently.

But just for comparison of large economic regions (> 100-200 Million people each) it would be useful

Maybe I'll try this myself (and hopefully submit a PR)