Add Parent/Child selection to CloudCare

[FB ticket](http://manage.dimagi.com/default.asp?125678) / [QA ticket](http://manage.dimagi.com/default.asp?129570) / [Spec](https://docs.google.com/a/dimagi.com/document/d/1hQeyTqP8uHXRLk1x66IIeXdTC4J5D-fQEe3sjywpz8k/edit#heading=h.vthcylu009oo)

Adds parent child functionality to CloudCare. If a module is configured to "select parent first" and a form uses cases, then the user will be able to select a parent case and then a child case.