add unicorn configuration for production

[joshea0]

Description

TableXI has an example of the unicorn configuration they use for staging environments in config/unicorn/stage.rb. For our production deployment, we will need our own production unicorn configuration.

I am planning to keep most of their configuration, but replace some of the hard-coded values (e.g., the socket path) to use environment variables instead.

Related

If we decide to build a staging environment to mirror production (which would be a good idea), then we will want to customize the staging configuration as well (config/unicorn/stage.rb).