app_confbridge: Can now set the language used for announcements to the conference.

ConfBridge now has the ability to set the language of announcements to the
conference.  The language can be set on a bridge profile in
confbridge.conf or by the dialplan function
CONFBRIDGE(bridge,language)=en.

(closes issue ASTERISK-19983)
Reported by: Jonathan White
Patches:
      M19983_rev2.diff (license #5138) patch uploaded by junky (modified)
Tested by: rmudgett


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@400741 f38db490-d61c-443f-a65b-d21fe96a405b