Change initial tab to "Unread"

[flip-rossi]

Like Readeck's web UI, it'd be nice if the app could start in the "Unread" screen instead of "All".

[ajaypremshankar]

@jensomato are you okay if I take a look into this?

[jensomato]

@ajaypremshankar Great, I'd love to check out your pull request. Thanks for your contribution.