Issue

Highlights don't seem to store elements added to them.
When we cut and move a piece of highlighted text from one scene to another, the elements associated with that piece of text are not moved/copied with the text.

Proposal

Make highlights store elements associated with them. And when we cut and paste a piece of highlighted text from one scene to another, the elements should follow them/be moved or copied (in case the element is associated with other text in the scene) into the new scene.