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

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

emplace doesn't overwrite already existing collection, so this would lead to leaking memory

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

Also, don't add particle as daughter to its parents.

This addresses an issue with fully duplicated entries in the parents and
daughters relations for MCParticles. After this bugfix, only a single
entry for each parents is entered in the parents relations, similar for
daughters. More demonstrated behavior in pull request comments.

BEGINRELEASENOTES
- edm4hep: don't add particle as parent to its daughters, and vice versa
ENDRELEASENOTES

warnings like
-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : em0044
      issued by : G4VEnergyLossProcess::SetMinKinEnergy
Parameter is out of range: 0 it will have no effect!
  Process hIoni  nbins= 84 Emin(keV)= 0.1 Emax(GeV)= 100000
*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------

-------- WWWW ------- G4Exception-START -------- WWWW -------
*** G4Exception : em0044
      issued by : G4VEnergyLossProcess::SetDEDXBinning
Parameter is out of range: -2.14748e+09 it will have no effect!
  Process hIoni  nbins= 84 Emin(keV)= 0.1 Emax(GeV)= 100000
*** This is just a warning message. ***
-------- WWWW -------- G4Exception-END --------- WWWW -------