Reverted "Refs #23919 -- Removed obsolete __init__.py files in management command directories."

This reverts commit ccc25bfe4f0964a00df3af6f91c2d9e20159a0c2.

https://groups.google.com/d/topic/django-developers/GVHMH2ciAnk/discussion

docs/howto/custom-management-commands.txt

@@ -18,7 +18,9 @@ whose name doesn't begin with an underscore. For example::
         __init__.py
         models.py
         management/
+            __init__.py
             commands/
+                __init__.py
                 _private.py
                 closepoll.py
         tests.py