Introduced ZalandoNode, i.e. a node with an additional type. The type is
a combination of event entries the node represents. The biggest
advantage is that the special way to map values to indices is not needed
anymore: node ids are now created consecutively instead of using
globally unique prefixes.
Extended GraphDataStructure to enable creating new ZalandoNodes.
Adapted GraphGenerators and BatchGenerators to make use of the new
ZalandoNodes.