geo bounds aggregation DSL

This PR adds a new aggregation DSL option: `geobounds filter <filterName> wrapLongitude <true/false>`. Elastic search reference: [geo bounds aggregation](http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/search-aggregations-metrics-geobounds-aggregation.html).

Test case added & passes. I've used the new aggregation in a project I'm working on and it's all good. I'd appreciate you pulling this into elastic4s.