Monocle: always relayout on scale chose.
Monocle: PagesLayoutManager::GetScaleMode().
Monocle: save scale mode in the doc state as well.
Monocle: keep UI state in sync on doc state recover.
Monocle: better code reuse.
Monocle: fixed zoom in / zoom out behavior on fit modes.
Monocle: shortcuts for zooming.