Add read-only user API backed by ES

This PR includes some tests for the API, probably a good idea to wait on build, although I have ran the tests locally.

There are still some changes I plan to make to the API, but what I've got so far should be good to merge in.  I still need to incorporate a single item detail view, and actually filter the fields that tastypie returns (right now, the fields parameter doesn't actually do anything).