Organize events (#13)

* move internal events & remove unused events

* `TrackUnpublishedEvent` for local tracks

* update example since we have local track unpublish events

* use flutter_webrtc 0.6.9

example/lib/widgets/controls.dart

@@ -47,11 +47,7 @@ class _ControlsWidgetState extends State<ControlsWidget> {
 
   void _unpublishAll() async {
     final result = await context.showUnPublishDialog();
-    if (result == true) {
-      await participant.unpublishAllTracks();
-      // Force to update UI for now
-      participant.notifyListeners();
-    }
+    if (result == true) await participant.unpublishAllTracks();
   }
 
   void _muteAudio() {

example/pubspec.lock

@@ -110,12 +110,10 @@ packages:
   flutter_webrtc:
     dependency: transitive
     description:
-      path: "."
-      ref: master
-      resolved-ref: "32d83d85fa2faebcd37a19534f8a84273b12cbce"
-      url: "https://github.com/flutter-webrtc/flutter-webrtc"
-    source: git
-    version: "0.6.8"
+      name: flutter_webrtc
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.6.9"
   google_fonts:
     dependency: "direct main"
     description: