Add support for playing an audio file for caller and callee at start and stop...

Add support for playing an audio file for caller and callee at start and stop of monitoring (one-touch monitor).
Keep messages short, since the other party is waiting while one party hear the message...



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@115784 65c4cc65-6c06-0410-ace0-fbb531ad65f3