PNG is now a resource.

You can now load textures threaded.
PNG will now throw exceptions when errors happend
SpriteComponent is now working without billboarding.

src/Game/Game.cpp

@@ -25,6 +25,7 @@ Game::Game(int argc, char* argv[])
     ResourceManager::RegisterType<Model>("Model");
     ResourceManager::RegisterType<RawModel>("RawModel");
     ResourceManager::RegisterType<Texture>("Texture");
+    ResourceManager::RegisterType<PNG>("Png");
     ResourceManager::RegisterType<ShaderProgram>("ShaderProgram");
     ResourceManager::RegisterType<EntityFile>("EntityFile");
     ResourceManager::RegisterType<Font>("FontFile");