effort-sharing package usage

[sverhoeven]

The https://github.com/imagepbl/effort-sharing package is currently used to make the data the explorer app reads.

The package includes things that could be imported and used here, reducing the duplication.

• list of additional regions
• list of what countries belong to what groups (G20, EU, etc.)
• Compute region allocations on the fly #96

[sverhoeven]

The package uses iso3 country codes while the app needs iso2 to render flags. So we need a mapping or use iso3 for flags.

[Peter9192]

In imagepbl/effort-sharing#119 @chantalwuer suggested to use the CountryConvert, which I think could be a really nice alternative for managing regions/countries/iso's etc.