app_meetme: Change app_meetme support level to extended from deprecated

(closes issue ASTERISK-20134)
Reported by: Leif Madsen
........

Merged revisions 370547 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@370548 65c4cc65-6c06-0410-ace0-fbb531ad65f3