DD4hepBuild: add -Wno-psabi to compiler flags to ignore warnings about ABI changes that we will never have issues with

As it stands, this project requires to find a python version matching
the one ROOT was build against EXACTLY. This has been discussed in #842.
This adds an option `DD4HEP_RELAX_PYVER` that will accept **any** python
version. It will then perform a custom check if major and minor version
of the ROOT python version and the one found match (in which it should
be safe to assume ABI compatibility). If not, it prints a warning but
continues with the build.

 - including necessary build macro etc

This reverts commit bea8748c.

Add examples of specialized shape views for CMS.
Simplyfiy grammar handling.

There was a bug in the dd4hep_add_test_reg function which was only taking into account the last dependency of a test when several were present.
On the way, dropped a double dependency in DDDB_clean_LONGTEST

also drop deprecated rootcling options

CMake: behave as before if BUILD_SHARED_LIBS is not defined. Needed for examples and DD4hep external packageS

CMake: add settings DD4HEP_BUILD_PACKAGES to chose which packages to build, DD4HEP_BUILD_EXAMPLES to build examples

it will be the responsible of the user to chose a working combination and order of packages
Use DD4hep::<Package> so that cmake will fail if required package was not enabled