Fixed design settings preview losing scroll position when changing settings
Fixed design settings preview losing scroll position when changing settings

refs https://github.com/TryGhost/Team/issues/1149

- replicated the visible iframe's `scrollTop` to the hidden iframe before swapping visibility between them so the scroll position remains consistent even though the contents and frames are fully reloaded and swapped

TryGhost/Ghost-Admin,TryGhost/Ghost-Admin