bookmark: introduce a 'applychanges' function to gather bookmark movement We want to track bookmark movement within a transaction. For this we need a more centralized way to update bookmarks. For this purpose we introduce a new 'applychanges' method that apply a list of changes encoded as '(name, node)'. We'll cover all bookmark updating code to this new method in later changesets and add bookmark move in the transaction when all will be migrated.