Add transfer softkey to ringout state to enable blond transfers.

(closes issue ASTERISK-21327)
Reported by: wedhorn
Tested by: myself
Patches: 
    skinny-blindxfer01.diff uploaded by wedhorn (license 5019)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@389164 65c4cc65-6c06-0410-ace0-fbb531ad65f3