Fixed #17794 - Added a bunch of cross-reference links to the DB queries topic…

Fixed #17794 - Added a bunch of cross-reference links to the DB queries topic documentation. Thanks guettli for the initial patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17624 bcc190cf-cafb-0310-a4f2-bffc1f526a37