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

example/lib/main.dart

@@ -1,10 +1,12 @@
 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) {