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

example/lib/main.dart

@@ -1,16 +1,14 @@
 import 'package:flutter/material.dart';
-import 'package:livekit_client/livekit_client.dart';
 import 'package:livekit_example/theme.dart';
 import 'package:logging/logging.dart';
 
 import 'pages/connect.dart';
 
 void main() {
-  print('This is a test for ${SignalTrickleEvent} test.');
   // configure logs for debugging
   Logger.root.level = Level.FINE;
   Logger.root.onRecord.listen((record) {
-    print('${record.level.name}: ${record.time}: ${record.message}');
+    print('${record.level.name}: ${record.message}');
   });
 
   WidgetsFlutterBinding.ensureInitialized();