Allow Bookmarks to be assigned to multiple folders

[Ford_Prefect]

Description:
It would be a totally handy addition if you could assign a bookmark to multiple bookmark folders. Assigning to a folder would be similar to how hashtags are currently assigned to bookmarks.

Practical example:
This would e.g. allow bookmarks to be 'contained' in a folder "A" as well as in a folder "B". Where folder "A" could be included in the bookmarks bar, but "B" could not. The same Bookmark could appear in the bookmarks menu on the desktop and/or only on mobile.