Sync when app opens [feature request]

[RayBB]

Per the discussion at tasks/docs#48
The app only syncs each hour in the background, 1 minute after creating/updating items, or when you pull to sync.

It would improve the user experience if the app syncs each time you open the app.
Perhaps it syncs if you open the app and it hasn't sync'd in the past 1 minute or something.

Thanks again for making this awesome app :)

[abaker]

68d80a5