Fix modpings schedule

[mbaruh]

• Fixes the modpings scheduler. Various bugs aside, key idea is that both caches are necessary to determine whether or not the moderator should currently have the role. Therefore almost all the checks, role changes, and scheduling are now under a central function handle_moderator_state.
• Adds the sync command in case there's some problem, and the status command to view current status, when pings come back, and what the current schedule is.

Since the relevant part of the code is rewritten, this PR also closes #2003