Adds Unicorn for production

Pivotal Tracker story: https://www.pivotaltracker.com/story/show/66233080

Related stories:
https://github.com/g5search/g5-content-management-system/pull/291
https://github.com/G5/g5-layout-garden/pull/19
https://github.com/G5/g5-widget-garden/pull/201
https://github.com/g5search/g5-theme-garden/pull/68