Fixed #14173 -- Added sections about contrib apps-provided commands to django-admin.py docs.

Added documentation about changepassword, pointers to GeoDjango, sitemaps and
staticfiles commands, grouped them by app.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14327 bcc190cf-cafb-0310-a4f2-bffc1f526a37