WIP: Component slots

[cmagill]

Feedback: "Easy mode" with components

@Matej This is pretty similar to one of my requests made on the idea board. I think the mechanism by which this can be achieved would be analogous to Gutenberg’s InnerBlock. Have an element that becomes an insertion point. At the point of insertion you select which components are allowed for selection. You can then move this insert point element anywhere within the component, have multiple of them, and have them nested. For the editor the insertion point would present a plus button which provide…