Polish the print spooler loading of stored print jobs.

1. The singleton print spooler isntance is created when the print spooler
   service gets a connection to the system and is destroyed when this
   connection is removed. Note that if the spooler has work, then the
   connection to the system will not be removed.

   When the spooler is created, it reads the stored state and notifies the
   system which in turn dispatches this to the print services.

   When the system connects to the spooler and passes it a connection, we
   schedule a delayed check whether there is work for the spooler. We do
   not handle this immediately to avoid intermitted spinning on and off
   of the spooler process if a client makes a sequence of queries while
   the spooler has really no work.

2. Fixed a bug in the NotificationManagerService where adding a notification
   and removing it immediately after that does not remove the notification.
   The code that is adding a notification is run on a handler thread while
   the code to remove it on the calling thread. This creates a race and
   erroneous results. Now the removal is also scheduled on the handler.

3. Many small fixes here and there.

Change-Id: I6415c253139fa6616393fbe23c659d031a29e1f6