Support bar plots

[DunklesArchipel]

The current version would support bar plots, where the x-axis contains a defined incremental increase of the value. The labels can, however, also reflect specific properties. Examples:

• Age distribution: 'Age 5-10', Age 10-20, Age 20-23
• Vehicles: Cars, Motorcycle, Bus, ...

In that case, the x-axis has to be constructed in a different way.