Add attr function for xercesc use, so that char arrays can be used to get xml elements (e.g., necessary to use ddsim w/ xercesc)

Include cmake module path for FindXerces
Forward the DD4HEP_USE_XERCESC variable and call DD4HEP_XML_SETUP
Forward DD4HEP_USE_BOOST and call find_package boost

Moved find_package to main cmakelists
use add_dd4hep_plugin to add library, create rootmap and install library
Moved xml_setup to main cmakelists

Moved find_package calls to main cmakelists
moved include_directories to main cmakelists
only use dd4hep_generate_rootmap

Split into apple and notapple functions, users just use dd4hep_generate_rootmap
removed commented code in generate_rootmap_apple

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

Phi2 is the deltaPhi in Geant4, it is the EndPhi in TGeo

It is necessary to copy most of the cmake content, if the installation directory is not the same as the source directory
In that case the cmake folder would be missing.

Move option calls before checking deprecated _WITH_ variables, otherwise _USE_ variables are overwritten when not set in command line

 - increased version number to v00-07

Add two cmake functions for creating dd4hep plugins (creating library and rootmaps and installing package env file)

   part of DD4hep, i.e. no external library option
   - however DDSegementationConfig is created for other packages to 
     build against it
 - changed library versioning of DDSegmentation to be in synch w/ DD4hep
   ( versions and so-versions)
 - some cleanup of geant4 stuff

Change options _WITH_ to _USE_
Print Warning that variables with _WITH_ are deprecated
Change Defintions to _USE_ as well
Add REQUIRED to find_package geant4 and xercesc if they are turned on
Updated documentation
Updated ILDExDet example

Export writes information in ~/.cmake/packages, making it hard for cmake not to find ddsegmentation (even when it is removed)

Rename DDSegmentation_INCLUDE_DIR to ..._DIRS
Fix standalone build of DDSegmentation, set DDSegmentation_LIBRARIES in DDSegmentationConfig.cmake
Keep the choice to use external DDSegmentation, set _LIBRARIES and INCLUDE_DIRS in DDSegmentation CMakeLists.txt in case of internal build

   in order to keep simple build sequence for DD4hep