Add option for logging congested calls as CONGESTION instead of NO_ANSWER in CDR

This patch adds a CDR option to cdr.conf that will allow CDR files to log calls ending
with congestion in a way that is unique from other unanswered calls.

(closes issue ASTERISK-14842)
Reported by: Alec Davis
Patches:
	cdr_congestion.diff.txt (License #5546) patch uploaded by Alec Davis


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@332760 65c4cc65-6c06-0410-ace0-fbb531ad65f3