Adds (somewhat crappy) controls to example game

sky/examples/game/main.dart

 import 'dart:sky';
 import 'lib/game.dart';
 import 'lib/sprites.dart';
 import 'package:sky/framework/app.dart';
 
 AppView app;
 
 void main() {
   // Load images
   new ImageMap([
       "https://raw.githubusercontent.com/slembcke/GalacticGuardian.spritebuilder/GDC/Packages/SpriteBuilder%20Resources.sbpack/resources-auto/BurnTexture.png",
       "https://raw.githubusercontent.com/slembcke/GalacticGuardian.spritebuilder/GDC/Packages/SpriteBuilder%20Resources.sbpack/Sprites/resources-auto/asteroid_big_002.png",
+      "https://raw.githubusercontent.com/slembcke/GalacticGuardian.spritebuilder/GDC/Packages/SpriteBuilder%20Resources.sbpack/Sprites/resources-auto/GG_blueship_Lv3.png",
     ],
     allLoaded);
 }
 
 void allLoaded(ImageMap loader) {
   // Create a new app with the sprite box that contains our game world
-  app = new AppView(new SpriteBox(new GameWorld(loader),SpriteBoxTransformMode.letterbox));
+  app = new AppView(new GameBox(new GameWorld(loader)));
 }