Add the AccountCode header to the AMI Hangup event.

It's harder to correlate the Newchannel and Hangup AMI events without
specifying "AccountCode" in both.

(closes issue ASTERISK-19963)
Reported by: Oleg A. Arkhangelsky
Patches:
      hangup_acctcode.diff (license #6397) patch uploaded by Oleg A. Arkhangelsky


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@370309 65c4cc65-6c06-0410-ace0-fbb531ad65f3