Added a new 'statistics.json' endpoint to the ResourceMonitor, this
deprecates the old usage.json endpoint.

This is v2 of the monitoring statistics, added with a new 'statistics.json' endpoint.

The 'usage.json' endpoint is now deprecated, and will be removed at a later point.

From: Ben Mahler <benjamin.mahler@gmail.com>
Review: https://reviews.apache.org/r/11641
Updated 3rd_party licences in the LICENCE file.

Review: https://reviews.apache.org/r/11711