Tabbed case detail

See corresponding PR in commcare-odk.
Ah, I see it now, so you specify the nesting at the <detail> level rather than the <datum> level. Is the XML format for that actually in the doc? I don't see the list of detail definitions in there.

To confirm: the plan is to retain the distinction between the "list" detail screen and the "overview" detail screen, and either of those could contain some degree of nesting?