loadCsv = async (filename) => {
  return new Promise(resolve => {
    const url = `${BASE_URL}${filename}`;

    console.log(`  * Downloading data from: ${url}`);
    Papa.parse(url, {
      download: true,
      header: true,
      complete: (results) => {
        resolve(parseCsv(results['data']));
      }
    })
  });
}
Downloads and returns the csv.

@param {string} filename Name of file to be loaded.

@returns {Promise.Array<number[]>} Resolves to parsed csv data.