Moved BitField64 to DDSegmentation, which is now stand-alone

DDCore and other packages now depend on DDSegmentation
Segmentation from DDCore now holds a DDSegmentation object that is created during XML parsing
Readout interface extended to act like a full IDDecoder combining information from the volume manage and the DDSegmentation object
TODO: Segmentation could be removed completely, if Readout simply holds a DDSegmentation object
TODO: Missing DDSegmentation classes for cylinders