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/constants.dart

@@ -0,0 +1,7 @@
+class Timeouts {
+  static const connection = Duration(seconds: 5);
+  static const debounce = Duration(milliseconds: 100);
+  static const publish = Duration(seconds: 3);
+  static const iceConnection = Duration(seconds: 5);
+  static const iceRestart = Duration(seconds: 10);
+}