Implements the new `CHATHISTORY LISTCORRESPONDENTS` API.

See #1603

1. Use FAIL instead of WARN
2. Use NICKNAME_RESERVED instead of ACCOUNT_REQUIRED
3. Don't send 433 at all for registered clients, just send the FAIL

List IRCv3 CAPs in `NS CLIENTS LIST` output

Send a WARN NICK ACCOUNT_REQUIRED on attempt to take a reserved nick

All truncation must be made UTF8-safe.

AWAY status should be tracked per-session:

1. With auto-away enabled, away status is aggregated across sessions
   (if any session is not away, the client is not away, else use
   the away status that was set most recently)
2. With auto-away disabled, we get the legacy behavior where AWAY
   applies directly to the client

Implement the new bot mode spec:
https://github.com/ircv3/ircv3-specifications/pull/439

RELAYMSG should respect mutes

Improve error message for CS TRANSFER

PerstentStatusMandatory should display as "enabled", not "mandatory",
in the context where it refers to a user-chosen setting.

Allow chanops to delete channel messages from history

Handle panics in rehash, even if it was triggered by SIGHUP

Implements #1577, but the issue should remain open until we clean up
the debugging loglines.

Fixes #1064.

make PASSWORD an alias for PASSWD in nickserv

1. Send COMPLETE_CONNECTION_REQUIRED instead of DISALLOWED
2. Include the account name in all FAIL messages

ERR_INVALIDMODEPARAM should take both the mode and the invalid parameter
as arguments.

As of #1483, websockets entail enforce-utf8, so there's no need
to check globalUTF8EnforcementSetting when handling websockets.

Improve debuggability of some config deserialization errors

1. Text and binary frames are accepted
2. Text frames are sent by default
3. Binary frames are sent to clients who negotiate `binary.ircv3.net`
4. Non-UTF8 data is not accepted (enabling websockets still enables UTFONLY)

ZNC playback LIST was panicking when history was disabled,
and possibly in other cases

If history is disabled, disable the history CAPs

Fixes #1510

Make snomask add/remove behavior match other ircds

Transition most "is an operator" checks to require a specific operator
capability

CS OP should regrant one's stored amode

Let halfops change the channel topic

Registered channels should be eagerly created on startup, and should
remain (and be visible in LIST) even when they have no members.

Track channel join times, use them to optionally enforce history access
restrictions