Add default-user-modes configuration to conventional.yaml.
Fix comment on DefaultUserModes.

It was only initialized for always-on clients, not for regular clients.
This explains a lot in terms of #812 failing to reproduce.

also, handle nickname targets in znc.in/playback

Explicit quit and ping timeout behave the same way,
but reattach after abandoning/losing the previous session
(without the break being detected server-side) is more aggressive
about replaying missed messages, at the cost of potential duplication.

In the k8s PROXY-before-TLS setting, we don't know all the IPs
of the load balancers, so we can't whitelist them, so they're at
risk of being d-lined.

1. If both fingerprint and hash are specified, require both instead of either
2. Implement auto-oper on connect

* 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