Countries chart: clickable buttons legend

[breki]

On some countries chart Slovenia is an outlier and, when shown, hides information about the rest of the countries. A switch to hide Slovenia should be provided (probably somewhere in the lower right corner).

Redesign the legend to be represented by clickable buttons, like we do it on other charts.

[lukarenko]

We do not need that if we move the legend below the chart (horizontal) to make it similar to other charts and then teach users (or hint) that they can deselect there