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

pubspec.lock

@@ -99,11 +99,11 @@ packages:
     dependency: "direct main"
     description:
       path: "."
-      ref: use-custom-webrtc-build
-      resolved-ref: "4942e7faec2e5775d35c42e22c2929ca6ca53769"
-      url: "https://github.com/livekit/flutter-webrtc"
+      ref: master
+      resolved-ref: "32d83d85fa2faebcd37a19534f8a84273b12cbce"
+      url: "https://github.com/flutter-webrtc/flutter-webrtc"
     source: git
-    version: "0.6.7"
+    version: "0.6.8"
   http:
     dependency: "direct main"
     description: