Complete redesign of the segmentation business:

- DDSegmenation now comes with its own factory and with generic access to segmentation parameters
- Removes the necessity of implementing different XML parsers in DDCore
- DD4hep::Segmentation becomes a lot simpler and its Object is now following a standard decorator pattern, completely removing any need of messing with the vtable
- compact2lcdd works for example with BarrelCalorimeter from CLICSiD example (other examples need to adapt their XML to valid segmentation names)
- See also examples/Segmentation/SegmentationTest for stand alone example
- The segmentation names and their parameter names do NOT follow current SLIC conventions. Once SLIC depends on DDSegmentation this will work transparently.