Better audio management (#10)

* add audio_session package

* `AudioManager` initial design

* try to integrate audio manager

* configure audio session

* `DisposeAware`

disposing if already published causes exception.

* organize

* guard flutter_webrtc calls

* websocket async fix

* use `ConnectionState` instead of `_isClosed` and `isReconnecting`

* change create audio track defaults

* update protos

* protocol 3 speaker updates

* fix exception

* emit `RoomDisconnectedEvent` only once

* fix exception

* keep track of local / remote audio tracks

* explicit types

* manage track state

* re-structure audio management

* change defaults

* unpublish all

* use experimental build

* change defaults

* configuring is optional

* call native `RTCAudioSession.setConfiguration`

* defaults adjustment

* iOS only for now

* use lib 92.4515.07

* clean up

* revert audio options for now

* remove pod source

* rename apple related audio

* `createListener` method

* organize native audio

* `SpeakingChangedEvent` only on `Participant`

* refactoring

* fix ios compile

* fix configure audio only for iOS logic

* minor fix & clean up

* change dispose logic

* format protos

* fix unpublishTrack

* `createListener` into a mixin

* simplify

* use flutter_webrtc master

* unpublish for example

* update ios icon

* android icon

* web icon

* favicon

lib/src/track/video_track.dart

@@ -5,6 +5,7 @@ import 'track.dart';
 
 /// A video track will notify when its mediaTrack has changed.
 class VideoTrack extends Track {
+  //
   rtc.MediaStream _mediaStream;
 
   VideoTrack(
@@ -27,9 +28,12 @@ class VideoTrack extends Track {
   }
 
   @override
-  Future<void> stop() async {
-    await super.stop();
-    await _mediaStream.dispose();
+  Future<bool> stop() async {
+    final didStop = await super.stop();
+    if (didStop) {
+      await _mediaStream.dispose();
+    }
     // _mediaStream = null;
+    return didStop;
   }
 }