Kinesis Elasticsearch sink

Ah finally all those TODOs make sense. A package object would be great. Can you put that in?

There's an easy shuffle to do this:

```
cd src/main/scala
mkdir com.snowplowanalytics.snowplow.storage.kinesis
git mv com.snowplowanalytics.snowplow.storage.kinesis.elasticsearch com.snowplowanalytics.snowplow.storage.kinesis/elasticsearch
touch com.snowplowanalytics.snowplow.storage.kinesis/package.scala
```