Leak of graphics memory due to not destroying FilamentAsset

[dfinn]

RenderableInstance uses the AssetLoader class to create FilamentAsset instances (createAssetFromBinary(), createAssetFromJson(), etc). However, when these RenderableInstances go out of scope these FilamentAsset instances are not destroyed. Probably, SceneForm should destroy them by calling AssetLoader::destroyAsset() rather than requiring the user to do this. Failure to call destroyAsset() results in a (potentially very large) memory leak.

Potentially this could be done in RenderableInstance.detachFilamentAssetFromRenderer().