Scene Serialization dropping Sprite Component

## Bevy version

0.6.0

## Operating system & version

Ubuntu 20.04

## What you did

I tried to use the scene.rs example code to serialize and load a scene which had entities with the Sprite component. On load (after calling world.clear_entities) the Sprite component was missing off of the entity and the Image Handle was missing its reference.

## What you expected to happen

Saving and loading the scene should result in no change

## What actually happened

The sprite becomes invisible as its component is missing

## Additional information

Here is a repo showing the bug (saving is mapped to P and loading is mapped to L on the keyboard), loading multiple times seems to make the image handle find the image on alternating loads.

https://github.com/mwbryant/weird_loading_bug

This also happens with TextureAtlasSprite and when using binary serialization techniques.