add a defaults file containing all defaults for configuration options and tidy initial config

script/update_process_concurrency.rb

@@ -8,7 +8,7 @@ hash = {
       'quantity' => worker_quantity
     },
     'fast' => {
-      'quantity' => Postal.config.fast_server ? 1 : 0
+      'quantity' => Postal.config.fast_server.enabled? ? 1 : 0
     }
   }
 }.to_yaml