Add message interface for updating queue active/priority

This is in addition to the existing service-based interfaces, and enables remotely changing message_queue_node parameters.

Given its intended use, I chose to use the queue_id from the config files, rather than the topic name.

(As part of the coexploration project, I've written a GUI that is used to send these messages and monitor the status messages published by !32 (merged), so the user has an easy way to look up the topic -> ID mapping.)