Need a friendlier UI for rolling back changes at the area level

[boutell]

You can undo any change via Page Versions, but this is not the friendliest way to bring back that widget you just removed.

We could override the undo/redo keys, in which case we're taking over responsibility for that from ckeditor, which normally does a fine job, but only for the current text editor, not for widgets.

Or we could provide a separate undo/redo mechanism which would leverage the page version history and thus be able to undo widget deletes and the like.

[boutell]

Assigning to Kyle to think about the interface design but I'm sure @colpanik and @stuartromanek and @tquirino will have input.