Add Human Evaluation from inside Evalite

The idea is:

• You would specify a special humanScorer() in the scores array passed to evalite()
• In the UI, you could mark the result with a tick or cross
• This would be saved to a local JSON file, keyed under the eval name, input, expected and output. (this means that if the input, expected or output changes, the human score would be invalidated)
• The UI would then retrieve this JSON information where needed to display the scores.

Start at the evalite() scores array and the UI flow described in the issue, then trace how scores are stored and displayed. Define the humanScorer() interface and local JSON keying before connecting the UI tick or cross to persistence. Done means human marks are shown and retained, and changing the eval name, input, expected value, or output invalidates the saved mark.