Add a /status endpoint for accounts

See discussion on hawkular-devel
http://lists.jboss.org/pipermail/hawkular-dev/2015-November/001783.html
and also https://github.com/hawkular/hawkular-alerts/commit/53dafd419c5165f6fe4620d8d09ec64a6d068cbf on how Alerts did it.
I can imagine that the code to determine the version could even live in the commons repo