give all tasks a creation date. When to-dos are completed, if they're
sitting in "completed" section for more than 3 days, delete them on
cron. @sabrecat @paglias @colegleason @wc8 heads up. this should help
with the performance issues people are experiencing when they don't know
to clear completeds, but let me know if this you think this is a bad
idea. @wizonesolutions sorry for the delay ;)