RwLock order enforcement

The order in which the RwLocks are currently acquired in `meeting` is not enforced. The order:
1. `vote_auth`
2. `voters`
3. `admin_auth`
4. `invite_auth`
is only in that order because it was the most practical. Deadlocks could easily arise from changes to endpoints locking in another order (eg `voters` then `vote_auth` would deadlock with the logic in `start-vote`). The order could (and probably should) be enforced at compile time https://www.youtube.com/watch?v=Ba7fajt4l1M&t=1115s

The chances of deadlock is currently quite small, since the system is currently maintained my me, and I know what the order should be, but this should be seen as a future-proofing enhancement.