mostDeviant should detect the deviant series across a list of series

As it is at the moment it does not do what it is advertised "the average across all metrics passed is determined, and then the average of each metric is compared to the overall average".

The mean across all the series provided has to be used for the comparison, that allows to compare metrics with the group average which seems to be the purpose, as it is at the moment it just seems to be selecting those series with the highest standard deviation, but no comparison accross metrics happens.