Improve average spend metric

Improve the accuracy of the average spend metrics. Currently the most recent month is counted as a full month which artificially pulls down the average.

2 suggested improved metrics (i think 1 is the best but potentially more difficult to implement than 2)

1) Take the spend for the last 90 days and divide by 3. So if you're halfway in August take the spend for August to date, July, June and half of May. 

2) Dont divide the spend by 3, but 2+fraction of current month. So halfway through August you take spend for August, July and June and divide by 2.5