Implement fast simulation shower modelling. Simplify GFlash to use the same sensitive actions as fast simulation

Allow for sensitive actions with multiple readout segmentation in the Geant4Sensitive action sequence

Add user defined framework context to DDG4and make the G4RunManager instantiation a plugin this should consequently allow for user defined specializations.

Add test to dump hits from MultiSegment-MultiCollections example. Investigate issue: https://github.com/AIDASoft/DD4hep/issues/141 for details

 - removed random lines drawn in teveDisplay
 - dont't print DetectorData by default in dumpdetector

 Added one 'Geant4ScintillatorCalorimeterAction' into DDG4 plugins Geant4SDActions for  scintillator to take Geant4 BirksLaw effect as sensitive detector active layer.

Create stringstream to avoid changing output format for cout

No code changes. Common code formatting removing tabs, replacing with spaces (tab-size=-2) + emacs reformatting.