Add class distance to null rejection coefficient translator. This commit adds classDistanceToNullRejectionCoefficient(), a function that converts (label-specific) class distances into the units of the null rejection coefficients. That is, it does the inverse of the calculation that converts null rejection coefficients to null rejection thresholds. It also adds a getSupportsClassDistanceToNullRejectionCoefficient(), which indicates whether or not the given classifier actually supports the classDistanceToNullRejectionCoefficient() — i.e. overrides it with a proper implementation.