Select the correct deck after sync in fragmented mode.

[Issue 1235](https://code.google.com/p/ankidroid/issues/detail?id=1235)

The currently selected deck might change after a sync. In fragmented mode, the selected deck is updated in the fragment but not in the deck list. This ensures both are updated after a sync ends.

I found a bit of code that programmatically selects the deck (and thus loads a new StudyOptionsFragment) and factored it out for use in other places.