Add configuration option for the max number of results returned by an ElasticSearch index query

There may be times when limiting the result set size of an ElasticSearch index query to the currently fixed value of 100,000 results is not desired.  If you have a large dataset hosted on a machine capable of handling a large number of results the ElasticSearchIndex will currently 'truncate' your result set to a fixed value that may be too small (or large).  This pull request allows for the max result set size to be configured.

This change was tested with the following configuration:

```
Configuration conf = new BaseConfiguration();
conf.setProperty("storage.backend","berkeleyje");
conf.setProperty("storage.directory","/tmp/titan_test");

conf.setProperty("storage.index.search.backend", "elasticsearch");
conf.setProperty("storage.index.search.hostname", "localhost");
conf.setProperty("storage.index.search.client-only", "true");
conf.setProperty("storage.index.search.max-result-set-size", "500000");

TitanGraph graph = TitanFactory.open(conf);
```