Any kind of list or modular component nested inside the existing modular components widget

So having a widget that allows modular components (what we have here [https://github.com/netlify/netlify-cms/pull/1857](https://github.com/netlify/netlify-cms/pull/1857)) is really nice. But it doesn't seem all that useful to me unless I can nest another modular component block or a list widget inside of that.

As of right now, if you try and nest a list or modular components widget inside, there is no ability to "create new" data. The parameter of "create:true" doesn't seem to be working.

Ideally, it would be nice to be able to do something like this in the config.yml:

```- label: Content Blocks
name: contentBlocks
widget: list
types:
- label: Nested Modular Component
name: nestedModularComponent
widget: list
types:
- {label: lorem, name: ipsum, widget: string}
- label: Nested List
name: nestedList
widget: list
create: true
fields:
- {label: lorem, name: ipsum, widget: string}```