Lists of Controls?

Great project!

`https://avh4.github.io/elm-debug-controls/` demonstrates how to create, view, and interact with (click on and change) a `UploadRequest`, but how would one create and view a `List UploadRequest`? It would be great to be able to have a list of N `UploadRequest`s all of which are interactive. That's what I am trying to do with my own model. I have a record like:

```
type alias Record = {
name: String,
notes: List String,
things: List Thing
}

type alias Thing = {
one: String,
two: Int
}
```

It's not clear to me from the documentation and code how do to this. I saw that there is a "list" Control, but that doesn't do what I am trying to do, and I haven't been able to figure out exactly how to do it. I'm having a bit of a hard time wrapping my head around exactly how all of this works -- I'm a good developer with functional experience so a lot of it makes sense, but the overall approach is translucent to me currently (though, I can see that it is very cool).

Thank you!

Start with the linked elm-debug-controls demo and the existing "list" Control, then compare their behavior with the requested List UploadRequest and interactive Thing records. The issue does not name source files or tests; done would require a clear approach for creating and viewing a list of interactive records, along with documentation or an example showing that approach.

Written by the indexing model from the issue text.