(closes#3036)
1. Fix the modal close button icon - was not visible
2. Use a blocking modal for the Save/Restore dialog
3. Don't allow `context.save()` while modal is visible
(especially for `onbeforeunload` event - this would wipe user's saved
history if browser is closed while the Save/Restore modal was visible)
4. Don't allow blocking modals to be dismissed by pressing escape
5. Don't show the close button icon for blocking modals
Bryan Housel
7930a0bb36