[Core] Expose 'topic' service

Expose 'topic' services, which supports updating telemetry
subscriptions on mutation for WTD-1329.

platform/core/bundle.json

@@ -189,6 +189,10 @@
                 "key": "throttle",
                 "implementation": "services/Throttle.js",
                 "depends": [ "$timeout" ]
+            },
+            {
+                "key": "topic",
+                "implementation": "services/Topic.js"
             }
         ],
         "roots": [