'stats were not collected yet' situation should be better exposed in UI

From @tomek:

As for the two subnets, I think stats hook was not loaded on those two machines. It's a demo configuration error, not stork bug. But I agree that the situation can be handled a little bit better. @godfryd, @vicky, how about displaying a yellow warning that stats could not be retrieved and explain what the admin can do about it? Does it require any extra hook? Or is this a problem with the same subnet being handled by two servers?

ref: #47 (closed) and #47 (comment 115095)