Fix 2090: Sort decks in drop-down menu

To solve [2090](https://code.google.com/p/ankidroid/issues/detail?id=2090) I need advice from someone familiar with the Anki internals. What would be the best way to get a sorted list of decks? The logic in `DeckPicker` is dependent on the broader task: opening the collection, deleting a deck, syncing. How about `deckDueList`?