Switch to new event system (#9)

* `SignalEvents` and `synchronized` mode for `EventsListenable`

* cascade syntax

* clean up

* `RoomEvents`

* `ParticipantEvents`

* all events implemented

* make it compile with M1 macs

* dispose logic

* cleaner connect logic

* ask to publish

* fix initial EngineTrackAddedEvent glitch

* fix unpublishTrack bug

* clean up

* better events docs

* organize event types

* clean up

* cleaner wait logic

* wait for event instead of using Completer

* notifyListeners

lib/src/track/video_track.dart

@@ -1,12 +1,10 @@
-import 'package:flutter/foundation.dart';
-import 'package:flutter/material.dart';
 import 'package:flutter_webrtc/flutter_webrtc.dart' as rtc;
 
 import '../proto/livekit_models.pb.dart' as lk_models;
 import 'track.dart';
 
 /// A video track will notify when its mediaTrack has changed.
-class VideoTrack extends Track with ChangeNotifier {
+class VideoTrack extends Track {
   rtc.MediaStream _mediaStream;
 
   VideoTrack(