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

just in case this might give similar compilation problems as for DDCond

also remove where visited the $ statements in the files. They are useless, since git does not support them.
Fixed some tests, which no longer properly worked in the conditions area.

Support for multi-threaded Geant4 applications using DDG4Details are described in the release notes.