Upgrade to Rails 4.0.2

Well, that was fun. Time to play with streaming!
Enable turbolinks

It's fast and appears to work. Cool!
Minify assets in production

TODO: gzip them too.
Store admin user id in session rather than whole object

I've been getting some cookie overflows lately and I suspect it is
because serializing activerecord objects sucks. So instead this just
stores the ID of the logged in user in the cookie.
Update some strong parameters stuff
Add rails_12factor gem

Hopefully this will make assets work on heroku?
Use Cloudfront for assets

A bit of an experiment, we'll see how this goes.