Allow reproducing a specific image from a batch

[tazlin]

Batches create images that are currently only reproducible from using batch again. However, it is possible, using the LatentFromBatch node to generate only one (or more) image from a batch, without having to do the entire set. For example, if you generate 20 images, it is possible (using this node) to generate only images 16-18 (3 images total, without doing all 20).