Fixed #14693, #14709 -- Backwards incompatible change to rectify the confusion around the STATICFILES_URL and STATICFILES_ROOT settings.

  * Two new global settings that will be used by -- **but are not limited to** -- the staticfiles app: STATIC_ROOT and STATIC_URL.

  * Moving the 'django.contrib.staticfiles.templatetags.staticfiles' template tag to the core ('django.templatetags.static') and renaming it to 'get_static_prefix'.

  * Moving the context processor 'django.contrib.staticfiles.context_processors.staticfiles' to the core ('django.core.context_processors.static') and renaming it to 'static'.

  * Paths in media definitions will use STATIC_URL as the prefix if the value is not None, and falls back to the previously used MEDIA_URL.

Thanks again to the community for constructive criticism and Carl and Russ for sanity-inducing discussions on IRC.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14592 bcc190cf-cafb-0310-a4f2-bffc1f526a37