stackedAreas needs to be reviewed

[KevCaz]

Currently there are too many options and the way the user can customize should be reviewed:

• pickcolors should be reviewed (it is not as useful as I thought)
• colors plaette must be removed and a call to another function should be used instead (see Add new color palettes #5 )
• an argument such as add_legend should be added to know whether or not a default legend is desired, currently the way legend is handled is not satisfying at all.