Switch to kaminari for pagination

This will make it easier to debug and correct pagination- related
performance issues as we're now using the same pagination system for the
frontend as we are for the rails_admin backend.
Remove Rack::Timeout so that ruby-level timeouts can be configured in one place
load unicorn only in appropriate environments
Make the database timeout configurable via ENV
Remove newrelic monitoring for now
Remove airbrake / errbit exception catching
Remove delayed_job
Make production rails log levels configurable