extension: automated level/page bookmarks for quick address bar access

Should be a triggerable setting (i.e. bookmarks seamlessly added/removed at any time) and those should follow the player's progress (new page recorded -> new bookmark if enabled).

Furthermore, players ideally should also be able to choose where (globally or just for individual riddles?) and how frequent (once per level's front or for every navigated page, including eggs?) those should appear.