Add warmup parameter for Heart Rate Drift

[Gregory Smith]

Heart Rate Drift on the statistics page uses the HR normalized for avg power in the first half of the workout versus the second half of the workout. I checked a published description for the parameter and it indicated that you should compare the HR for first half vs second half after the HR has come up to a steady training value. I think that we would have more accurate drift readings if we added a parameter that set a fixed “warmup period” for the beginning or workouts. This sets the amount of time to ignore from the beginning of the workout. The remaining workout time would be divided in two and then compared using the existing formula.