Fixed #15252 -- Added static template tag and CachedStaticFilesStorage to staticfiles contrib app.

Many thanks to Florian Apolloner and Jacob Kaplan-Moss for reviewing and eagle eyeing.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16594 bcc190cf-cafb-0310-a4f2-bffc1f526a37