use new case processing in 5% of the domains

@dannyroberts should have context for this.

Also adds a new type of toggle that can do deterministic randomness

http://manage.dimagi.com/default.asp?146788

Also adds an admin-only UI for viewing the enabled toggles for a domain.
![image](https://cloud.githubusercontent.com/assets/66555/5050060/ec6279a6-6bf8-11e4-9a04-85c4ddb1b5f6.png)

And minor tweaks to edit toggle UIs for something that is randomly set.

![image](https://cloud.githubusercontent.com/assets/66555/5050078/05848410-6bf9-11e4-9056-6ac8d38e8f56.png)

The only non-admin-facing change is: https://github.com/dimagi/commcare-hq/commit/d4ce65280c8d56f58bdc24b8be116306cfc6421c

see you found the tests - added a doc string as well