New package for Grafana (1.5.2)

Installs into `/usr/share/grafana` like a good little webapp. We can point
an Nginx vhost to that directory, and probably override `config.js` with a
location block.

---

Example build here: https://launchpad.net/~gds/+archive/test-govuk/+sourcepub/4080615/+listing-archive-extra