MessageDirector: Move thread-safety requirement to the MDUpstream.
MessageDirector: Fix -Wreorder warnings.
Tests: Add a few cases of sleep(0.1) to mitigate some race conditions exacerbated by the new threading model.
Tests: Add another sleep(0.1) to CA tests to mitigate another race condition.
Merge branch 'enhancement/threading' into enhancement/database-overhaul
Database: Move responsibility for thread-safety and proper operation-concurrency handling to the backend.