GitLab

- ideally should move to using key4hep

	modified:   DDG4.py

 - Use dump to print all constants, their values, and inputs.

no cache docker image build

	modified:   src/dd4pod/plugins/Geant4Output2Podio.cxx

	modified:   src/tools/CMakeLists.txt
	modified:   src/tools/include/clipp.h
	modified:   src/tools/src/npdet_info.cxx

	modified:   npdet_info.cxx

- root dropped geocad from their code base, which some tools were built
  on. This was added to a new library build.
- Added geocad library build
- New cmake flag USE_GEOCAD is automatically set if OpenCascade is
found.
- executable under `tools`, `npdet_to_step` is now available

	modified:   contents.rst

	modified:   .gitlab-ci.yml
	modified:   doc/Doxyfile

- a job now generates the dd4pod data model.

- a job now generates the dd4pod data model.

Also moved from using the sodium --> silicon runner.

 -  moved containers to `.containers`
 - updated docker tag to use the VERSION file.

- Renamed `GenericDetectors` -> `detectors`
- Removed `ConceptDetectors`. Full concepts should live outside of this
 repository. The  only full detector concepts should be within the
 context of `examples`.
- New version number 0.4.0

	new file:   VERSION

	modified:   RomanPot_geo.cpp

	modified:   ../src/GenericDetectors/trackers/src/RomanPot_geo.cpp

- Units are in GeV and mm

- Clean up of podio yaml file

	modified:   .gitlab-ci.yml

Adding unit testing

See merge request !145

	modified:   plugins/Geant4Output2Podio.cxx

Acts V1 changes

See merge request !144

	modified:   ConceptDetectors/topside/CMakeLists.txt

	modified:   ../GenericDetectors/CMakeLists.txt

npsim - a ddsim wrapper

See merge request !143