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

Allow to set ambient temperature and pressure for all materials. With examples/ClientTests/compact/Check_Air.xml -- scripts/Check_Air.py

Add properties to Geant4GDMLWriteAction to steer writing of regions, cuts and sensitive detectors. See github issue https://github.com/AIDASoft/DD4hep/issues/507

Add properties to Geant4GDMLWriteAction to steer writing of regions, cuts and sensitive detectors. See github issue https://github.com/AIDASoft/DD4hep/issues/507

Add properties to Geant4GDMLWriteAction to steer writing of regions, cuts and sensitive detectors. See github issue https://github.com/AIDASoft/DD4hep/issues/507

Add properties to Geant4GDMLWriteAction to steer writing of regions, cuts and sensitive detectors. See github issue https://github.com/AIDASoft/DD4hep/issues/507

Fix hundreds of std=c++11 compiler warningsAllow to change compiler settings in cmake/DD4hep.cmake valid for all packages.Watch out for CMAKE_CXX_FLAGS in cmake/DD4hep.cmake.Move to use Boost spirit::phoenix version 3. ---- Prepare for ROOT 6

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