Add new admin features to meetme: Roll call, eject all, mute all, record in-conf

This patch adds the following in-conference admin DTMF features:
*81 - Roll call (or simply user count if INTROUSER isn't enabled)
*82 - Eject all non-admins
*83 - Mute/unmute all non-admins
*84 - Start recording the conference on the fly

FWIW, this code uses newly recorded prompts.

(closes issue #16379)
Reported by: rfinnie
Patches:
      meetme-enhancements-232771-v1.patch uploaded by rfinnie (license 940)
      modified slightly by me


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@260757 65c4cc65-6c06-0410-ace0-fbb531ad65f3