Add time period to usage_data.rb

In usage_data.rb, include a time period. This could be week-over-week or for the current/past calendar month.

The current month to date and also the last full calendar month would be best, or even incrementally the last 12 calendar months of data. From a performance standpoint, we should establish when would be a good stopping point.

e.g. all of April and May 1st > 28th.

@tayloramurphy @jeremy @donaldcook @jameslopez Does this make sense? Are there any issues to this approach?