* change NPSimulation structure to allow conditional compilation

   + geant4 files are kept in the include and src directories
   + one directory is created for each detector. This directory
     contains the associated headers and sources files
   + a script directory is created with some scripts allowing the
     conditional compilation

 * Add #ifdef statements in DetectorConstruction.cc file
   + this applies to each detector header

 * Move G4MultiFunctionnalDetector.hh header from Sharc.cc to 
   Sharc.hh