Import historical data.

@brad So here is what I have for importing historical data. You can see in the view code where it should be imported, but having that call there was breaking tests. (Looks like a Celery issue.)

I tested everything manually with your Misfit credentials, and it's looking good. No unit tests because mocking all of those api calls looks kind of painful, and I ran out of time to do it today.
@grokcode Do we need to wrap this block in a `try..except` or do you think we're safe? In my experience, I've seen the celery queue crash completely when an uncaught exception occurs, then I have to restart the queue manually (if I even notice it has stopped)