Promise to wait for an image to have loaded

[severo]

We could use https://developer.mozilla.org/en-US/docs/Web/API/HTMLImageElement/decode#Examples instead of https://github.com/LyonDataViz/occupapp/blob/07624ea038016dc67d56021811f17e7fb4227707/src/utils/img.ts#L5...

[severo]

fetchImage = src => {
  const img = new Image();
  img.src = src;
  return img
    .decode()
    .then(() => img)
    .catch(encodingError => {
      // Do something with the error.
      throw new Error(`Image ${src} could not be loaded: ${encodingError}`);
    });
}