elasticsearch returner

Fixes #10678
Dependencies:
- [official elasticsearch python client](http://elasticsearch-py.readthedocs.org/)
- jsonpickler

configuration is defined in the master config file:

```yaml
ext_job_cahe: elasticsearch

elasticsearch:
    host: 'some.host.com:9200'
    index: 'salt'
    number_of_shards: 1 (optional)
    number_of_replicas: 3 (optional)
```

**Note**: WIP in title will be removed once ready for merging. 

- [x] code
- [x] documentation