[1.2.X] Fixed #14173 -- Added sections about contrib apps-provided commands to...

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

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

Backport of [14327] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14328 bcc190cf-cafb-0310-a4f2-bffc1f526a37