Add notifications by webhook.

Add a new config entry moving to version 13.
```
		"webhook": {
			"1": {
				"enable": true,
				"address": "http://requestb.in/1i9al7m1"
			}
		}
```

cmd/notifiers.go

@@ -40,6 +40,8 @@ const (
 	queueTypePostgreSQL = "postgresql"
 	// Static string indicating queue type 'kafka'.
 	queueTypeKafka = "kafka"
+	// Static string for Webhooks
+	queueTypeWebhook = "webhook"
 )
 
 // Topic type.
@@ -61,6 +63,7 @@ type notifier struct {
 	Redis         map[string]redisNotify         `json:"redis"`
 	PostgreSQL    map[string]postgreSQLNotify    `json:"postgresql"`
 	Kafka         map[string]kafkaNotify         `json:"kafka"`
+	Webhook       map[string]webhookNotify       `json:"webhook"`
 	// Add new notification queues.
 }
 
@@ -102,6 +105,18 @@ func isNATSQueue(sqsArn arnSQS) bool {
 	return true
 }
 
+// Returns true if queueArn is for an Webhook queue
+func isWebhookQueue(sqsArn arnSQS) bool {
+	if sqsArn.Type != queueTypeWebhook {
+		return false
+	}
+	rNotify := serverConfig.GetWebhookNotifyByID(sqsArn.AccountID)
+	if !rNotify.Enable {
+		return false
+	}
+	return true
+}
+
 // Returns true if queueArn is for an Redis queue.
 func isRedisQueue(sqsArn arnSQS) bool {
 	if sqsArn.Type != queueTypeRedis {