Fix auditorium JOIN lines with zero values for the time and msgid tags.

Configurations with require-sasl and open account registration are valid,
but likely unintended. Show a warning about them.

1. Fix auth bypass in the default configuration with the addition of
   server.password (the REGISTER command was allowed before connection
   registration, allowing unauthenticated users to REGISTER and then
   take advantage of skip-server-password)
2. Caution operators against the use of require-sasl without disabling
   user-initiated account registration. (Such a configuration is still valid
   in the case of a public server that requires everyone to register.)

Allow users to set max MySQL connections and connection lifetime;
set a sane default for max connections if it's not present.

I broke this in #1615 / 0d05ab4ff4

Fix incorrect description of channel ownership in NS INFO

Remove the CHATHISTORY * and znc.in/playback *self targets,
clean up associated database code, add new mechanisms to play
all missed DMs.

Remove debugging loglines for truncation

Allow setting the minimum TLS version

Prevent LUSERS stats from getting out of sync when modes are
modified on offline clients.

Allow snomasks to be added via oper config block, even if the oper
doesn't have `ban` or `snomasks` and therefore can't add snomasks
on their own.

Clean up channels during unregistration if necessary.

Warn users that NS UNREGISTER doesn't give them a "do-over";
the account name will remain reserved.

UBAN ADD and DEL need to produce snomasks and loglines

Document permissions structure of CS AMODE

CS INFO with no arguments should list your registered channels

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.