Provide scorers that use binary judgments the mapping of values to relevant or irrelevant

[david-fisher]

Is your feature request related to a problem? Please describe.
As a relevance engineer, I would like to evaluate my binary judgment metrics, such as precision or reciprocal rank, on cases that have multi-valued judgments.

Describe the solution you'd like
I would like to specify a separate parameter in the settings menu that passes the mapping choices (max irrelevant value for scales, or a map) in the same fashion as qoption is passed in for individual queries to the scorer.

This would allow implementing a single scorer for a metric, eg:
presumes #1259

RR@k

const k = get_k() 
let rank = 0;
const max_irrel = get_max_irrel()
eachDoc(function(doc, i) {
    if (rank === 0 && hasDocRating(i) && (docRating(i)) > max_irrel) {
        rank = i+1; // remember the rank of the first relevant document
     }
}, k);
const score = rank > 0 ? 1.0 / rank : 0.0;
setScore(score);