Links to Grafana

We need a better intergration with Grafana. For the time being we could add the following:

• ability to open Grafana in iframe. This is lightweight and would look as visually integrated solution. (I've attached a mockup of how this could look like). @godfryd tried this and it was infeasible due to XSS protections. WE opted to go with dedicated links on stork pages.
• for the demo in April, the link could be hardcoded
• for the 0.7 release, we could have the Grafana (and Prometheus) links configurable in the db.