New Relic Store/Source - first pass

Use the existing logic from the newrelic branch, and bring it up to speed with the new store/source format.

This store type doesn't *have* to have a specified application_id, but the separation in new relic exists for a reason.
Sanitise some newrelic metric names

For some reason, some metrics come with colons, and braces. Insufficient newrelic documentation to deal with braces at this time, so ignore them
capture socket errors in newrelic endpoint
Merge pull request #64 from anchor/new_newrelic

New Relic Store/Source