Capistrano-based deployments

@ajshort I propose that we're using Capistrano for deployment. I'm a noob in that area, so just cobbled together something to start off with. What do you think?

In terms of env specific SS config, I'm copying a `staging.yml` or `production.yml` file which contain different index names for elastic search. Can you think of a smarter way to do this?

I don't really like having deployment files in the app repo itself, maybe something like [caphub](https://github.com/railsware/caphub) would be more appropriate, but it gets us started for now.