Don't wait forever for Growl 2.x on-click/timeout notification which will never come.

Background: http://njr.sabi.net/2013/08/07/growl-and-pester-repeating-alarms/
Change the less-than-useful "Stop Alerts" button in Notification Center alerts into a "Stop Repeating" button.

Add alarm UUIDs so we have a persistent handle for alarms across launches.

Register the NSUserNotificationCenter delegate at startup so we can handle "Stop Repeating" while Pester is not running.

Remove the delete-by-index methods from PSAlarms, which were never used, and replace it by an access-by-UUID method.
If OS X notifications are enabled on <10.8, explain why they don't do anything.