Change places where the name "INBOX" was hardcoded to use the imapfolder

setting from voicemail.conf instead. This commit will help to get issue
#11415 moving towards commitment.



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@93094 65c4cc65-6c06-0410-ace0-fbb531ad65f3