api: Implement bucket notification. (#2271)

* Implement basic S3 notifications through queues

Supports multiple queues and three basic queue types:

1. NilQueue -- messages don't get sent anywhere
2. LogQueue -- messages get logged
3. AmqpQueue -- messages are sent to an AMQP queue

* api: Implement bucket notification.

Supports two different queue types

- AMQP
- ElasticSearch.

* Add support for redis

vendor/gopkg.in/olivere/elastic.v3/uritemplates/utils.go

@@ -0,0 +1,13 @@
+package uritemplates
+
+func Expand(path string, expansions map[string]string) (string, error) {
+	template, err := Parse(path)
+	if err != nil {
+		return "", err
+	}
+	values := make(map[string]interface{})
+	for k, v := range expansions {
+		values[k] = v
+	}
+	return template.Expand(values)
+}