10. As an item, I want my estimated next purchase date to be computed at the time my purchase is recorded in the database so the app can learn how often I buy different items.

[stacietaylorcima]

AC:

• When a purchase is recorded, the estimated number of days until the next purchase date should be calculated and recorded in the database

The script at /src/lib/estimates.js should be used to calculate the next estimated purchase interval.