Some updates for salome_on_demand:

Some updates for salome_on_demand:
minimize environment variable of base modules at the start:
     we need only the pythonpath to the python script who launche salome

Install all external binaries in salome_common_dir "__SALOME_EXT__/SALOME"

update Salome_Common_env.py for salome tools and prerequisites

remove the SALOME sub-directory from SALOME_EXT

remove subdirectory SALOME from SALOME_EXT

Base_env.py:update for common directory of extensions

Create 3dparty package including all of prerequisites of salome

update to minimize salome launcher dependencies