Make sure linechart is required before any subclasses are
Move out voronoi data generation to own function

needed if the data is different that it used to be for the linechart
Introduce area chart for easy stacked area charts

subclass from linechart to use all the features a lnechart got
including vornoi selection of points
use default data key values:
y and y0 for values
name for group name
Add military civil firedensfoerderung viz

use subnav concept for friedensfoerderung
Add legend
Merge pull request #95 from okfde/65-layeredareachart

Friedensfinanzierung