Stop clobbering detailed BodyMedia data

After running the `*_day` synclets, the `*_year` synclets would rewrite the
dates on their next run with less detailed data. Because the `_day` version had
marked the day done, it would never get recrawled. This prevents the `_year`
version from returning data for days that have been crawled by `_day`.

As a side note, these synclets are nearly identical and should be refactored.
Because we crawl forward in time, we could probably just store the latest date
too, rather than the whole set of finished days.
Merge pull request #815 from Singly/fix-bodymedia

Stop clobbering detailed BodyMedia data