Move Json.Upgrader out of Sandbox,Game, have it filter by type
Add GameResource.ResourceVersion
Inject version into gameresource saves
Change DeserializeToObject to use JsonNodes
GameResources can define JsonUpgraders
v1 upgraders for SceneFile and PrefabFile
Add GameResource.LoadFromJson and use that anywhere we load a GameResource
Fix PrefabFile upgrader doing nothing
Fix tests, supply upgraders