add Capistrano for deployment

@rrmait0, this branch adds Capistrano for deployment. I tried to organize the deploy.rb file into an app-specific, a server-specific section (which over the long term should probably be moved elsewhere), and a section that should be more-or-less identical for anything (well, any Rails app) we wish to deploy. (I snuck in the mysql2 gem, since we needed that anyway.)