Use receiver names from config (#34)

* Use common configuration format of 'receiver_name' -> 'receiver_config'

* Adjust receiver configuration files

receivers.json

@@ -1,8 +1,8 @@
-[
-    {
+{
+    "natsrecv" : {
         "type": "nats",
         "address": "nats://my-url",
         "port" : "4222",
         "database": "testcluster"
     }
-]
+}