PagerDuty improvements

Found occasionally incident's would be formated as 'undefined'. It turned out that it was from incidents from email-based services.

This fixes the `formatIncident` to show subject information if provided. It also cleans up that method a bit so there's less redudant code, and also will show at least incident number & creation date if there's not extra info. It also adds a command to show any old incident, which was useful in debugging this.