[ENH] improve figure output

[Remi-Gau]

• the current figures are hard to understand and could probably be improved
• might require to play with different figure style options

[Remi-Gau]

From the original README:

Not much is done in statBuilder.create_plots() to make the image look better and clear when a lot of plots are shown at once.

[JRandy77]

The current system has you specify how many graphs wanted for each measure. This results in weird behavior where not all identifiers will have all graphs generated for them. All identifiers should be displayed by default.