Cleanup/refactor rubycloud scroll

-- Extract html5_shiv to its own scroll
-- Extract imgsizer to its own scroll
-- Extract respond.js to its own scroll
-- Move blank.gif to fancybox & imgsizer where they
   are actually needed
-- Rename jquery.rails back to the original name (jquery_ujs)
   because other scrolls and generators may use it as a marker
   (such as foundation)
-- Move a bunch of stuff from after_everything to after_bundler
   in the rubycloud scroll
-- Update ZURB foundation to verison 4 (this will likely require
   a few more tweaks)