Allow Adding Existing Node Types on Layout Page

Headline:
It’d be nice to be able to add existing node types to a layout from the layout page.


Description:
It’d be nice to be able to add existing node types to a layout from the layout page. Currently, the only way to do this is to edit the layout and associate it to a node type. Adding an option under the “+ ADD” to add an existing node type, or a separate button would be nice.