Now just call it once when needed, otherwise it comes from the DD4hepConfig
This ensure that we do not create the Target when re compiling dd4hep packages

Move find_package xercesc to dd4hep_xml_setup, so all the xml treatment is in one place
Move find_package boost and lcio to main cmakelists, so they are done once and not repeated
Move include geant4_use_file to main cmakelists, so all of the geant4 treatment is in one place