Save verse-level scores for test.py

[mshannon-sil]

We want to save the scores (including confidence if it's being saved) for test.py at a verse-level automatically, rather than having to run diff_predictions afterward. Currently only It can be similar to how write_sentence_bleu works, but saving all the scorers used not just sentence_bleu. We can reuse the name that method uses: test.trg-predictions.detok.txt.[ckpt].scores.tsv.

Once that's done, we also need to change the quality_estimation script so that it takes in this file rather than diff_predictions as an input.