Previously was overloading operator(), now is constructField()

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

This parameter is needed to not have single steps attempting to reach 1km (the
default, see
https://geant4.web.cern.ch/geant4/UserDocumentation/UsersGuides/ForApplicationDeveloper/html/ch04s03.html
). This can happen for low energy curlers in the beam pipe vacuum.

Add this also to DDG4 setup and to documentation example for field
get default value in case it is not set

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.