WHISTLE-1720: remove busted cancel clause
WHISTLE-1720: move some types into the queue manager

WHISTLE-1720: spec update

WHISTLE-1720: track the enter_when_empty flag

If there are no agents known to the queue manager, check the flag for
whether to allow the caller to enter the queue (or cancel the call).
WHISTLE-1720: add unavailable as an agent change state

WHISTLE-1720: send queue updates on agent changes for login/out

WHISTLE-1720: reject the member call if empty and flag is false

WHISTLE-1720: change to targeted publish

WHISTLE-1720: process member_cancel in callflow

WHISTLE-1720: remove log line

WHISTLE-1720: let queue manager know about config change

WHISTLE-1720: track whether new calls should be allowed in the queue if no agents are logged in (but maybe busy).

WHISTLE-1720: include the call id in the retry message

WHISTLE-1720: remove busted cancel clause