Add forecast count into cumulative count

[kathsherratt]

? This should solve the problem of decreasing cumulative totals (https://github.com/reichlab/covid19-forecast-hub/pull/2447)

• includes re-formatted submissions which are still open PRs in the forecast-hub

[seabbs]

Haha whoops - nice catch. Would it make more sense to do a cumulative sum of the forecast rather than add as lagged values?