Refactor returnWeeklyLongestSleepers(week) to take metric and add onto it for aboveAverageSleepers

[hfaerber]

SleepRepo

Line 13 - returnAboveAverageSleepers(week)
and
Line 43 - returnWeeklyLongestSleepers(week)

We can refactor into one method that takes the metric as a parameter. We may still need to have a method to find above average sleepers but it could just call the refactored method and add onto it.