Multiple changes:

- Split up UI into several files
- Handle connection state better
- Add images
- Granular rebuilding of state dependent widgets
- Fix usage of alert dialogs
- Add some basic theming
- Add dialog for adding multiple links at once

lib/api/commands.dart

@@ -1,16 +1,16 @@
 import 'dart:convert';
 
-sealed class ConnectionEvent {}
+sealed class PlayerConnectionEvent {}
 
-class Connect extends ConnectionEvent {
+class Connect extends PlayerConnectionEvent {
   final String uri;
 
   Connect(this.uri);
 }
 
-class Disconnect extends ConnectionEvent {}
+class Disconnect extends PlayerConnectionEvent {}
 
-class Command extends ConnectionEvent {
+class Command extends PlayerConnectionEvent {
   final String type;
   final Map<String, dynamic> value;
 

lib/api/events.dart

@@ -1,7 +1,6 @@
-// TODO: handle typing and deserialization of events
 import 'package:flutter/foundation.dart';
 
-import '../state/player_state.dart';
+import 'package:gergle/state/player_state.dart';
 
 // NOTE: see DEFAULT_PROPERTY_SUBSCRIPTIONS in the websocket API source for greg-ng.