Test material mapping

This branch was derived from the testDD4hepPlugin branch and therefore contains also the geometry building example and extrapolation through a detector with DD4hep input. Furthermore it includes an example of the material mapping with DD4hep input. First the material maps are created from the full DD4hep geometry using Geant4. Then the material is mapped onto the simplified ACTS geometry (which is directly translated from DD4hep using the DD4hepPlugin) using the MaterialPlugin. Afterwards two tests are done to test the material. First a LayerTest, which writes out the Geant4 Material assigned to a layer and the ACTS Material assigned to a layer. Second a full material test which writes out the full ACTS material which can be compared with the original Geant4 material. To write out the different material maps several root writers have been introduced. Finally root scripts to create histograms, compare the materials, write out the error... have been introduced which use input of the writers.