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

DDSim: compactFile can only be one instance, otherwise we cannot overwrite what is in the steeringfile, still takes multiple XML files

From https://stackoverflow.com/a/41153081

Needed for python2.7 compatibility

The XML files need to follow the structure where at the end is a closer file.
compactFile takes multiple arguments, or multiple instances of compactFile or both.

  ddsim --compactFile $DD4hep/examples/CLICSiD/compact/SiD_multiple_inputs.xml $DD4hep/examples/CLICSiD/compact/SiD_detectors_1.xml --compactFile $DD4hep/examples/CLICSiD/compact/SiD_detectors_2.xml $DD4hep/examples/CLICSiD/compact/SiD_close.xml --runType shell

Per #883 diquarks are treated as stable by geant4 but they can have nominally non-zero travel times inside an event graph and should be explicitly rejected.

this worked accidentally in python2, but now the dictionary order is fixed and isotrop was set to false when parsing the default values, because it happens after the setting of distribution now