Viewer metrics api (#208)

* Add support for ending the inbound stream. Closes #191

* Add a simple success response to API requests

* Add viewers over time API

* Move controllers to admin directory

metrics/timestampedValue.go

@@ -0,0 +1,8 @@
+package metrics
+
+import "time"
+
+type timestampedValue struct {
+	Time  time.Time `json:"time"`
+	Value int       `json:"value"`
+}