Add BitmapManager class

src/app/gfx/bitmap.cc

@@ -94,7 +94,7 @@ void Bitmap::Create(int width, int height, int depth, Bytes data) {
   width_ = width;
   height_ = height;
   depth_ = depth;
-  data_ = data;
+  data_ = std::move(data);
   pixel_data_ = data_.data();
   surface_ = std::unique_ptr<SDL_Surface, SDL_Surface_Deleter>(
       SDL_CreateRGBSurfaceWithFormat(0, width_, height_, depth_,