Permanently dismiss the "service added" message in the inspector.

As suggested by Luca, the message is dismissed per-model, meaning
it's not shown again for the single service inspector.
Merge pull request #626 from frankban/dismiss-service-added

Permanently dismiss the "service added" message in the inspector.

As suggested by Luca, the message is dismissed per-model, meaning
it's not shown again for the single service inspector.