Configuration option "enableLink" not available in iFrame mode

[mrdsam]

Make option "enableLink" available in iFrame mode, too

There's an option "enableLink" (at least in version 2.0)

enableLink 	Optional. Enable/disable graph with a rendered URL to the Grafana dashboard. Defaults to yes.

It is marked as 'optional', not as 'Proxy mode only Optional', so I would expect it to be available in iFrame-Mode also.

In version 1.4.3, I did a quick and dirty patch to add this feature. When I tried to do this for version 2, I discovered that this feature is already there.

[mrdsam]

Uh, there's a pull request already, #300, never mind!