ENH: display more information in MonteCarlo prints and plots

[Lucas-Prates]

Here are some suggestions to enhance our prints and plots in the MonteCarlo class

Prints

• 95% Prediction Intervals (implementation suggestion: use the numpy's quantile function to compute the percentiles 2.5% and 97.5%);
• Median;
• Maximum and minimum;

Plots

• Boxplots and density plots shown together with the already existing histograms (see this to understand how it would look like);