[feature][DUNE_ENABLE_PYTHONBINDINGS] Added cmake option for enabling

Python bindings, default is OFF.

CMakeLists.txt

@@ -23,8 +23,12 @@ dune_project()
 add_subdirectory("dune")
 add_subdirectory("doc")
 add_subdirectory("lib")
-add_subdirectory("python")
-dune_python_install_package(PATH python)
+
+# if Python bindings are enabled, include necessary sub directories.
+if( DUNE_ENABLE_PYTHONBINDINGS )
+  add_subdirectory("python")
+  dune_python_install_package(PATH python)
+endif()
 
 # finalize the dune project, e.g. generating config.h etc.
 finalize_dune_project(GENERATE_CONFIG_H_CMAKE)