WHISTLE-1510: don't convert tuples to lists
WHISTLE-1510: start conference using uuid_transfer instead of sendmsg

Should address and close WHISTLE-1816 too
WHISTLE-1510: use is_boolean test in validator
WHISTLE-1510: support ad-hoc conferencing, make prompts optional
WHISTLE-1510: update schema with new prompt flags
WHISTLE-1510: formatting
WHISTLE-1510: friendly name for another error case
WHISTLE-1510: use boolean atoms instead of binaries
WHISTLE-1510: add support for other prompt toggles