De-listing

Currently, there's no reliable way to pull an item out of a list once it's there. 

When you're on a list item and you hit the button for the same list type, pull that item out of the list as a paragraph at the root level and split the list. 

To make this usable, we also need to be sure that turning that element back in to a list joins the list back up (but doesn't necessarily indent it to its previous level).