WHISTLE-1510: massage some of the conference commands, and add recordstop
WHISTLE-1510: maybe emulate channel_execute/_complete for conference play commands
WHISTLE-1510: add recordstop to conference APIs
WHISTLE-1510: add recordstop to whapps conference commands
WHISTLE-1510: use the exand api if we have a call id to play to
WHISTLE-1510: relay conference events to ecallmgr_fs_nodes to publish to AMQP
WHISTLE-1510: flush conference cache on disconnect
WHISTLE-1510: encode local stream filename for play
WHISTLE-1510: add say, tts, tone to conference commands
WHISTLE-1510: add some optional fields to some dialplan commands
WHISTLE-1510: add delete_keys/2 to props module