Implement Elasticsearch output connector

It would be great to be able to write data to Elasticsearch (bulk) API.

This connector should use the ES the ES HTTP client, not TransportClient (TC has issues with things like different client vs. server library versions, so should be avoided and the ES HTTP client, written in Java, was written to avoid these TC issues)

Once such connector exists one could use it not only writing to their own ES cluster, but also services that expose the ES API, like Logsene (http://sematext.com/logsene) and others.