Notify the application when an ISS occurs

[poulok]

Create a new notification to be sent via the NotificationEngine that informs the application when a self-ISS is detected. This should probably be an async notification. The notification must include the round number that has the ISS.

[timfn-hg]

@poulok Will we ever care about the other types of ISS events (e.g. "catastrophic" and "other") or solely just self events?

[poulok]

Great question. Yes for catastrophic and self ISSes, but not for non-fatal ISSes in which the self node is in the majority.