Fixes #15270 -- Moved back the serve view to django.views.static due to dependency conflicts with the contrib app staticfiles (reverts parts of r14293). Added a helper function that generates URL patterns for serving static and media files during development. Thanks to Carl for reviewing the patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15530 bcc190cf-cafb-0310-a4f2-bffc1f526a37