Remove ElasticSearch global, pass it as argument
Pass es as keyword argument es_
Pass es object through base class _build_query*

Passing this everywhere feels cleaner to me than asserting it isn't
None and passing it as a keyword parameter.
Merge pull request #80 from openannotation/deglobalise_es

Deglobalise es
Bump version to 0.12dev
Make flask an extra
Update CHANGES.rst