Email reminders

Even though I work on the Carbon Diet every day, I often forget to add new data every week. Because of this, I've added an "email reminder" option in the user profile. If you enable it, the site will email you each week (or as often as you choose) if you haven't entered data for a while. The default is off, so it won't annoy anyone who hasn't turned it on explicitly, but it should be useful I think!