getStackedSeriesTotals(excludedSeriesIndices = []) {
    const w = this.w
    let total = []

    if (w.globals.series.length === 0) return total

    for (
      let i = 0;
      i < w.globals.series[w.globals.maxValsInArrayIndex].length;
      i++
    ) {
      let t = 0
      for (let j = 0; j < w.globals.series.length; j++) {
        if (
          typeof w.globals.series[j][i] !== 'undefined' &&
          excludedSeriesIndices.indexOf(j) === -1
        ) {
          t += w.globals.series[j][i]
        }
      }
      total.push(t)
    }
    return total
  }
@memberof CoreUtils
returns the sum of all individual values in a multiple stacked series
Eg. w.globals.series = [[32,33,43,12], [2,3,5,1]]
 @return [34,36,48,13]