Expose registration and related component interfaces to extensions (#1322)

Signed-off-by: Lauri Nevala <lauri.nevala@gmail.com>

src/extensions/core-api/index.ts

@@ -10,6 +10,7 @@ import * as EventBus from "./event-bus"
 import * as Store from "./stores"
 import * as Util from "./utils"
 import * as ClusterFeature from "./cluster-feature"
+import * as Interface from "../interfaces"
 
 // TODO: allow to expose windowManager.navigate() as Navigation.navigate() in runtime
 export let windowManager: WindowManager;
@@ -18,6 +19,7 @@ export {
   App,
   EventBus,
   ClusterFeature,
+  Interface,
   Store,
   Util,
 }