Options group management

[Issue 1591](http://code.google.com/p/ankidroid/issues/detail?id=1591)

This will add options group management, including:
- Add
- Remove
- Rename
- Reset to default
- Apply group to all subdecks

Most options group management operations can trigger a card reordering, which takes time, so I've added new DeckTasks for the ones that do. Note that desktop Anki [doesn't reorder cards yet](https://anki.lighthouseapp.com/projects/100923-ankidesktop/tickets/675) for these operations (except for reset), so the reorder logic is kept out of libanki.