Seperate internal/external implementation of segmentations. Remove some ID tags - do no longer make sense in git.

Added support for vector parameters in segmentations (int, float, double, string) which are simply space separated values in the xml element
Added TiledLayerSegmentation as an example for a complex segmentation that is calculated based on a volume ID

Added simple nearest neighbour calculation
Fixed compact XML of all examples to work with the new segmentation types

- 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.

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

Remove materials from LCDD. Look them directly up in the TGeoManager instance and avoid double caching.