epiweekly denominator forecasts

[dylanhmorris]

Right now, we forecast both the numerator and the denominator daily and aggregate to epiweekly as needed.

Given that percentage forecasts are likely to be viewed at the epiweekly scale and the denominator is modeled amechanistically, it may be more robust to fit a model of the epiweekly (versus daily) denominator and join in to the numerator forecasts only once they have been aggregated to epiweekly.