Save low res previews as metadata

[huntfx]

The ability to preview different profiles would be a lot faster and memory efficient if the metadata contained a pre-rendered small image. To keep filesize down, a config option should be provided.

On inactive profiles: The metadata should contain when the last render was made and compare it to the current state of the file. Render new image upon file load if they don't match.

On active profiles: Store image in memory and don't save (for ANY profile that has been loaded this session). If there is a backlog of commands, there could be issues with two saves on the same file happening at the same time.