* Fix#684
* Fix#683
* Add `CHANSERV CLEAR`
* Allow mode changes from channel founders even when they aren't joined
* Operators with the chanreg capability are exempt from max-channels-per-account
* Small fixes and cleanup
This moves channel registration to an eventual consistency model,
where the in-memory datastructures (Channel and ChannelManager)
are the exclusive source of truth, and updates to them get persisted
asynchronously to the DB.
As well, add channel registration and re-applying founder privs on the first client joining the channel. I'm going to re-architect our modes system to better acocunt for this sort of change.