confbridge: Separate user muting from system muting overrides.

The system overrides the user muting requests when MOH is playing or a
waitmarked user is waiting for a marked user to join.  System muting
overrides interfere with what the user may wish the muting to be when the
system override ends.

* User muting requests are now independent of the system muting overrides.
The effective muting is now the logical or of the user request and system
override.

* Added a Muted flag to the CLI "confbridge list <conference>" command.

* Added a Muted header to the AMI ConfbridgeList action ConfbridgeList
event.

(closes issue AST-1102)
Reported by: John Bigelow

Review: https://reviewboard.asterisk.org/r/2960/
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Merged revisions 402425 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 402427 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@402428 65c4cc65-6c06-0410-ace0-fbb531ad65f3