Rake task to sync with Pivotal Tracker

As a user
I want the system to update itself
So each morning, I get a fresh, up-to-date burndown.

Create  rake task for this; it's up to the use to trigger this task once a day (e.g. cron or Heroku Scheduler).

Each burndown contains project ids and a pivotal token. We need to deduplicate data here to avoid storing the same data for a project more than once.