calcurse: tag appointment alerts with app name and icon

Matches the other calcurse notifications, so dunst rules can target them.

.config/calcurse/conf

@@ -28,6 +28,6 @@ general.firstdayofweek=monday
 general.multipledays=yes
 general.periodicsave=0
 general.systemevents=yes
-notification.command=calcurse --next | xargs -0 notify-send "Appointment"
+notification.command=calcurse --next | xargs -0 notify-send -a calcurse -i x-office-calendar "Appointment"
 notification.notifyall=all
 notification.warning=3600