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/widgets/participant.dart

@@ -21,7 +21,7 @@ class ParticipantWidget extends StatefulWidget {
   State<StatefulWidget> createState() => _ParticipantWidgetState();
 }
 
-class _ParticipantWidgetState extends State<ParticipantWidget> with ParticipantDelegate {
+class _ParticipantWidgetState extends State<ParticipantWidget> {
   //
   TrackPublication? videoPub;
   TrackPublication? audioPub;