Production environment

refs #172 
and some informations below.
http://blog.livedoor.jp/maru_tak/archives/51247889.html
http://guides.rubyonrails.org/configuring.html

I enabled ```serve_static_asserts``` in production environment and it's a little bit bad for performance.
If we have enough time, we should disable that configuration and serve static files on HTTP server(Apache, Nginx, or Passenger).