confbridge: Add 'Admin' param to join, leave, mute, unmute and talking events

Currently there's no way to tell if a user is an admin or not when receiving
the join, leave, mute, unmute and talking events.  This patch adds that
capability.

Tested by: George Joseph
Review: https://reviewboard.asterisk.org/r/3950/
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Merged revisions 422176 from http://svn.asterisk.org/svn/asterisk/branches/12
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Merged revisions 422177 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@422178 65c4cc65-6c06-0410-ace0-fbb531ad65f3