Rename target to DDRec, this required changes in many other CMakeLists to be consistent

Re-arrange Gear dependent parts into single if scope
Add SYSTEM to GEAR IncludeDirs

Use variables to define libraries in one place and add optional ones (i.e., gear) to the list

Create plugin_sources variable to create a DDRecPlugin independent of the DDRec library parts

No Whitespace after and before parenthesis
Assume ROOT_INCLUDE_DIRS is added in main CMakeLists file
Comment Setting of CMAKE_CXX_FLAGS

    - in a next step the SurfaceManager will
      be re-written to be a singleton that
      caches surface lists and maps ...

 Update teveDisplay for better visualization resolution on Tube. For example TPC, Hcal outer shape and Coil.

   to be used to only build detector envelopes
 - fixed visualization in teve_display to also
   show the envelope volume
 - visualize daughter level in dumpdetector (tabs)

   shows all DetElements in model incl. #surfaces

   we need this application as it is the main simulation
   application for LC
 

   a DDG4 based simulation with xml configuration files
   (originally in DDSim)
 - renamed print_materials.cc to print_materials.cpp

Improved version of MC particle handler, fix calorimeter hit aggregation with multiple contributions

    - renamed namespace tgeo to dd4hep
       -> users need to replace tgeo::mm by dd4hep::mm

    to MaterialManager

  - improved utility print_materials to print material properties along  
    a straight line between two points including integrated radiation and 
    interaction lengths (useful for debugging geometries and materials)

  - use averaged material for Surfaces where the thickness extends
    beyond the volume

  - added release notes for material stuff

 - added simple utility print_materials.cc 
 - started to implement averaging materials for surfaces
    - issue with ILDExDet geometry and assemblies ...

     - draw sensitive surfaces in red and helper surfaces in gray
     - protect against missing lcio input file
  - reduced printout from VolumeManager  (changed INFO to DEBUG)