Subscriber as primary (#8)

* Update protos

* Signal client

* Improve transport

* First implementation

* Fix publish

* Update `PCTransport` for debounce negotiation

* debounce func

* reconnect & events

* Update debounce func

* engine events

* make sure events don't emit after dispose

* prefix flutter_webrtc

* Cleaner `iceServers` update

* don't mutate user provided params

* fix tests

* event manager

* Fix: `Room.onDisconnected` gets fired multiple times

* data publish in example

* cleaner logic

* safer events

* un-prefix with LK

* organize imports

* Clean up

* remove `Tuple`

* `EventsEmitter` can now be directly listened to

`EventsEmitter` extends `EventsListenable`

lib/src/track/_audio_api.dart

@@ -1,6 +1,6 @@
-import 'package:flutter_webrtc/flutter_webrtc.dart';
+import 'package:flutter_webrtc/flutter_webrtc.dart' as rtc;
 
-void startAudio(String id, MediaStreamTrack stream) {
+void startAudio(String id, rtc.MediaStreamTrack stream) {
   // do nothing
 }