Merge branch 'python_2_and_3' into develop

CMake/UseSWIGLocal.cmake

CMakeLists.txt

Documentation/Cookbook/rst/Installation_Linux.txt

Documentation/Cookbook/rst/Installation_Macx.txt

Documentation/Cookbook/rst/Installation_Windows.txt

Modules/Wrappers/SWIG/otb-module-init.cmake

Modules/Wrappers/SWIG/src/CMakeLists.txt

Modules/Wrappers/SWIG/src/java/CMakeLists.txt

Modules/Wrappers/SWIG/src/python/CMakeLists.txt

Modules/Wrappers/SWIG/src/python/itkPyCommand.cxx

Modules/Wrappers/SWIG/src/python/itkPyCommand.h

Modules/Wrappers/SWIG/src/python3/CMakeLists.txt

Packaging/CMakeLists.txt

Packaging/install_python_bindings.cmake

SuperBuild/CMake/External_otb.cmake

SuperBuild/CMakeLists.txt