add rmqstate module

this module contains some code from the management module. we're going
to periodically call list-queues and put the result on a core.async mult.

at the moment the management module still starts a thread for each
filesystem and calls list-queues in each of those threads.
start the rmqstate watcher when setting up the system
use go blocks instead of threads in manage-filesystem

this uses system's :looping-qwatcher in order to convey rmqstate's
list-queues result.