Active queue cleanup

Merge this after !27 (merged)

• Make service calls idempotent, rather than requiring the same number of disables as enables.
• Filter based on topic at time of encoding, rather than in the callback before enqueuing. Partial solution to #29.
• Misc cleanup for consistency

I have a test script that exercises these changes, and I'll create a merge request to the acomms_tests repo as soon as I have permissions.

I assign copyright to Woods Hole Oceanographic Institution, in order to get this thing merged. (Though I hope y'all are sorting that out!)