As per the discussion [in issue 1744](https://code.google.com/p/ankidroid/issues/detail?id=1744) and elsewhere on this PR, let's indeed remove "show whiteboard" from the actionbar, and I'll make the whiteboard state save on a per-deck basis so that this option is used less often. I think we should also boost up "show whiteboard" to just below "undo" as this will likely be the 2nd most used action when the whiteboard preference is enabled.