Support Elasticsearch "join" types

[jbaiera]

With the eventual removal of multiple types in one index, the handling of parent-child type data has changed a bit in Elasticsearch. There is a new join mapping type that allows users to model their data in a parent-child relationship without the use of different types. A few factors that ES-Hadoop must consider for this:

1. We must continue to support "parent" headings for legacy Elasticsearch versions.
2. Users should be able to specify that a field is considered a join field, and the connector should extract the routing information from the join field.
3. If a user specifies both a join field and a routing field, the routing field should be used if it can be found, and if not, the extraction should fall back to extracting from the join field.
4. When reading data, we must accurately parse both forms of the join field (String for parents / Object for children). This is doubly sensitive for the schema based integrations.

[jbaiera]

This is complete with the inclusion of 359026d