Calculate accuracy metrics by sex

[gregorgorjanc]

For X (and later Y and mtDNA) chromosome, but also autosomes, knowing the accuracy by sex can be informative - we expect higher accuracy on male side than on female side for X chromosome. Also, with autsomes we expect the same in animal breeding datasets because males have more relatives, hence more information - and generally there is less of sires, so this can make imputation easier overall.

@AprilYUZhang will look into this

We need to think how to present this as we already have too much information in accuracy tests - see #172