RFR: statsd ingestion endpoint.

A few things to know up front:

* Ingestion is a blocking HTTP operation (I'm amenable to changing this, but wanted feedback first).
* I punted on TTL, using a 48H default TTL for now.

Sample ingestion format is found in blueflood-http/src/test/resources/sample_bundle.json.

This PR is closely related to the statsd-backend that currently lives at https://github.com/gdusbabek/blueflood-statsd-backend.