Fixed PushServiceBase.Stop infinitely sleeping

Modified the PushServiceBase.QueueNotification method to only increment
the trackedNotificationCounter when a notification is actually queued,
as a MaxSendAttemptsReached failure scenario was NOT decrementing this
counter - causing the PushServiceBase.Stop method to sleep infinitely
when waitForQueueToFinish is true. Also modified the ApplePushService
class to implement Stop and clean up the Feedback timer task (which will
continuously run in the above bug scenario) when the base Stop method
completes execution