Note we're adding the icons in English on both the `sdg/en/` folder and
the `sdg/default/` folder. The latter stores the default icons when the
desired language does not have a fallback with an icon folder.
Also note we need to explicitely add the images to the asset pipeline
because they've been added to the `vendor/` folder; for some reason,
everything works properly without adding them to the asset pipeline if
we use the `app/` folder instead.
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