Fix a variety of memory leaks

This patch addresses the following memory/ref counting leaks:

 * main/devicestate.c - unsubscribe and join our devicestate message
   subscription
 * main/cel.c - clean up the datastore and config objects on exist
 * main/parking.c - cleanup memory leak of retriever snapshot on message
   payload destruction
 * res/parking/parking_bridge.c - cleanup memory leak of retrieve snapshot
   on message payload destruction
 * main/presencestate.c - unsubscribe and join the caching topic on exit
 * manager.c - properly unregister the manager action "BlindTransfer"
 * sorcery.c - shutdown the threadpool on exit and dispose of any wizards

(issue ASTERISK-21906)
Reported by: John Hardin
patches:
  cel.patch uploaded by jhardin (license #6512)
  devicestate.patch uploaded by jhardin (license #6512)
  manager.patch uploaded by jardin (license #6512)
  presencestate.patch uploaded by jhardin (license #6512)
  retriever-channel-snapshot.patch uploaded by jhardin (license #6512)
  sorcery.patch uploaded by jhardin (license #6512)



git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@392797 f38db490-d61c-443f-a65b-d21fe96a405b