Add support for RepeatContent within RepeatContent (or ListContent)

[biohazardxxx]

Adding a RepeatContent to a RepeatContent does not work.
It would be helpful to create a nested structure of text.

(n products, have n patches with n changes)
Otherwise nested ListContent would be an alternative to have nested ListContent blocks .

something like:

var valuesToFill = new Content(new RepeatContent("RepeatParentContent")
.AddItem(new FieldContent("Title", "Tests"),
new RepeatContent("RepeatChildrenContent", new FieldContent("SubTest", "WORKS!!!!"))
.AddItem(new RepeatContent("RepeatChildrenContent", new FieldContent("SubTest", "WORKS also!!!!")))
);