Core Persistence index & query with ElasticSearch

[Dave]

I've been working for the last couple of weeks on implementing index and
query in the new Usergrid Core Persistence engine, in the two-dot-o branch.

I've written up a summary of this work here in the Core Persistence design
doc:
     http://goo.gl/D9gqvV

Feedback, suggestions, core reviews, etc. are most welcome.

Thanks,
- Dave