Add implementation for signal handling. Use generic signal handler in DDG4 for controlled shutdown on CTRL-C. Add test DDG4_SIGINT_handler in examples/DDG4

default value is 700 micron, as is the default in geant10.1 as far as I can tell
Complete production threshold table is printed in DEBUG verbosity level

Support for multi-threaded Geant4 applications using DDG4Details are described in the release notes.

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

Add component to allow the setup of the magnetic field tracking in Geant4 from python. See DDG4/examples/CLICSidSimu.py for the usage.

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