seasonal mse stack plot

• calculate mse share of each season \text{mse}_{frac,season}=\frac{\text{mse}(season)}{\text{mse}(total)}
• Stackplot with 4 stacked bars, sum is equivalent to total mse, stacked bar elements correspondent to the fractional mse of each season
• caution: check if sum of seasonal mse is always 1 resp. total mse