add hq_user_id to CaseState

http://manage.dimagi.com/default.asp?146765

@czue how embarrassing 

This seemed like the least invasive option. Other options require an extra query to get the user_ids:
* update the `hqcase/by_domain_hq_user_id` so that you can get user_id's from case_id's
* update the SQL case index to include `hq_user_id` column
https://github.com/dimagi/commcare-hq/commit/b10aacb832d435eff83df938d9c3d68aa0fbdc40