PLT-4357 adding performance monitoring (#4622)

* WIP

* WIP

* Adding metrics collection

* updating vendor packages

* Adding metrics to config

* Adding admin console page for perf monitoring

* Updating glide

* switching to tylerb/graceful

einterfaces/metrics.go

@@ -0,0 +1,32 @@
+// Copyright (c) 2015 Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package einterfaces
+
+type MetricsInterface interface {
+	StartServer()
+	StopServer()
+
+	IncrementPostCreate()
+	IncrementPostSentEmail()
+	IncrementPostSentPush()
+	IncrementPostBroadcast()
+	IncrementPostFileAttachment(count int)
+
+	IncrementHttpRequest()
+	IncrementHttpError()
+	ObserveHttpRequestDuration(elapsed float64)
+
+	IncrementLogin()
+	IncrementLoginFail()
+}
+
+var theMetricsInterface MetricsInterface
+
+func RegisterMetricsInterface(newInterface MetricsInterface) {
+	theMetricsInterface = newInterface
+}
+
+func GetMetricsInterface() MetricsInterface {
+	return theMetricsInterface
+}