- updated Configuration to include ElasticSearch.
Add DiscoveryWriter and DiscoveryIO interface

The DiscoveryWriter class is used to record metric names to a backend
implementing the `DiscoveryIO` interface as new metrics come in. This
will later allow for querying for metrics using wildcards, as well as
getting a list of all metrics.
Initial commit of elasticsearch discovery backend
Make blueflood-elasticsearch a maven module
Move embedded ES server into tests so tests can find it
Do not use enum singletons