BoxSet represents one box-and-whiskers item. It takes five values to create a graphical representation
of range and three medians. There are two ways to give the values. The first one is with constructor
or with append method. In these the values have to be given in the following order: lower extreme, lower quartile, median,
upper quartile and upper extreme. The second method is to create an empty QBoxSet instance and give the values using
value specific methods.
\sa BoxPlotSeries