Add support for separate IndexCoordinates per query in multiSearch.

[AIRahimi]

The API

multiSearch(List<? extends Query> queries, List<Class<?>> classes, IndexCoordinates index)

takes an IndexCoordinates and sends in with each query in the multiSearch. ElasticSearch supports different indexes per query in the multisearch so we should be able to send in a list of IndexCoordinates that is iterated along with the query and class.

[AIRahimi]

@sothawo Can I solve this one my self? :)

[sothawo]

Feel free to create a pull request with the changes

[AIRahimi]

Done.