Feature Request: Support setting notification "interruptionLevel"

[npars]

I'm in a fairly large Github org and sometimes miss @mention notifications that are directed at me. It would be nice if trailer supported setting a different interruptionLevel for notifications based on some criteria (contains an @mention, your PR, etc.).

I poked around the codebase and noticed that Trailer is using NSUserNotification which is now marked deprecated and does not support setting the interruptionLevel like the newer UNNotification API. So unfortunately I think this would be a non-trivial change.