Add an elasticsearch query builder

Noah is using this for a feature he's working on and it seems relatively stable now, so I figure it's a good time to merge it in.  Happy to get feedback on it and iterate.  Includes tests.

The es_query file includes some documentation on usage, and you can see it in action by looking at tests.py.
I stuck an error check in the run method which instantiates this class.  That would probably make more sense here though.  Think the `__init__` method should raise?
https://github.com/dimagi/commcare-hq/pull/3879/files#diff-6bc5251ac254d50d65a8d33297cdd7fcR121