Add implementation for signal handling. Use in DDG4

[MarkusFrankATcernch]

BEGINRELEASENOTES
Add implementation for signal handling.

• The generic signal handler in DDCore may be used and specialized by applications as shon in the DDG4 package (see for details src/Geant4Kernel.h)
• Use generic signal handler in DDG4 for controlled shutdown on CTRL-C.
• Add test DDG4_SIGINT_handler in examples/DDG4
  to enable the signal handling use from python:

  geant4 = DDG4.Geant4(kernel, tracker='Geant4TrackerCombineAction')
  geant4.registerInterruptHandler() 
  

  Please note: The signal handler must be explicitly installed. DDG4 is a library framework and does not intervene in actions which users possibly want to handle themselves! This mechanism looks simple enough that it should not be annoying.
• This MR should implement issue#1330 and supposedly supersedes PR#1300

ENDRELEASENOTES

[github-actions]

Test Results

   14 files     14 suites   5h 38m 43s ⏱️
  367 tests   366 ✅ 0 💤 1 ❌
2 524 runs  2 523 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 9f258ce.