Tabbed case detail

FB129673

Technical spec: https://confluence.dimagi.com/display/ccinternal/Tabbed+Case+Detail

Not-so-technical spec: https://docs.google.com/a/dimagi.com/document/d/1MiGqDJA59ZN9ycEWuq5ObVc9lhpVe0TgwCAfInhDzF8
Added a comment. You'd have to save enough state (childDetail, entity, args) that I think it adds too much code to be worth it (unless we do find it contributes to bad performance, etc.).