Refactor the move line show that it is not a drag element, but a simple HTML Element.

Describe the new feature being added
To simplify our code we should have it the move line be a simple HTML element, rather than a drag element.

How will this feature improve this extension

Rendering the move line by making it a drag element will be confusing too future developers when they are looking at the codebase. This is because the move line doesn't actually get dragged on the page. It gets moved in discrete chunks when we cross the boundary of a row or column. It is more intuitive that this would be the job of a simple HTML element.