VoiceConnection rework (#1183)

* VoiceConnection rework

- improves codebase
- removes concept of pending connections
- attempts to fix memory leaks by removing EventEmitter listeners
- makes voice connections keep track of its own channel when it is moved by another user
- allows voice connections to reconnect when Discord falls back to another voice server or a region change occurs
- adds events for some of the aforementioned events

* Removed unused code

* More clean up / bugfixes

* Added typedefs to Status and VoiceStatus constants

src/client/voice/player/AudioPlayer.js

@@ -51,7 +51,7 @@ class AudioPlayer extends EventEmitter {
   }
 
   destroy() {
-    this.opusEncoder.destroy();
+    if (this.opusEncoder) this.opusEncoder.destroy();
   }
 
   destroyStream(stream) {