Clean up of the material manager... Removal of duplicated & unused code

• Remove the IGeoMaterialInterface & GeoMaterialManager code
• Refactor the MaterialManager

• Useage of IntrusivePtr
• Do not distinguish between GeoElement & GeoMaterial. In fact, the GeoMaterial->add method(GeoMaterial*) does behind the scenes nothing else than copying the elements from one object to another multiplied with the correspondning fraction
• The MaterialManager always branched such that the renormalization of the Elements is enabled if the first fraction is greater than 1. If not the materials are simply added without unity check --> Renormalize the element fractions

Tagging: @boudreau, @rbianchi, @tsulaia

I am thinking of whether we should move the MaterialManager back into GeoModelCore and then we can replace the Subdetector Material managers in athena with this.