update rails gem
use new auto-encrypted cookie_store
use new rails approach for storing secrets.
purposefully NOT committing new secrets.yml
Revert "use new rails approach for storing secrets."

This reverts commit c41f27e3699054984aa6b7dea4488830e489102c.
use spring gem to preload environment
:assets group removed in rails 4
add unicorn web server. clean Gemfile cruft.
Merge branch 'rails-4.1.0.rc1'
upgrade rails to edge!