'Queues and daemons' above for how to set this up.
enabled: Whether to uses queues. Defaults to false.
+daemon: Wather to use queuedaemon. Defaults to false, which means
+ you'll use OpportunisticQM plugin.
subsystem: Which kind of queueserver to use. Values include "db" for
our hacked-together database queuing (no other server
required) and "stomp" for a stomp server.