ES 1.2.1 support

This is for the 1.2.1 ES support issue: https://github.com/yakaz/elasticsearch-action-updatebyquery/issues/15

Most of the work was re-writing the REST Action class to use the new API instead of the older removed classes. SearchContext.close() will take care of the cleanAndRelease process that existed in the old function.

This builds and passes the test cases. Make sure that the elasticsearch setting is added to your config:
script.disable_dynamic: false

This would cause an issue with the update counter not working correctly in the response.