Commit 7ce396931c introduced the ability
that every user with an account in the AMODE list of a channel can use
the OP command to restore their modes. Update the chanserv help message
accordingly.

Users logged into an account can see their own email.
Opers with the accreg capability can see all users.

Sort snomasks for display rather than displaying them in hash order

This is a regression introduced in 0d05ab4ff4; playback for an individual
DM target would play all DMs.

If the relay bot and the owner share an IP, legacy bots that identify users
by user@host could misinterpret relayed lines as coming from the bot owner.
Try to avoid this by using the bot's account cloak where applicable.

Send a full NUH with RELAYMSG.

Also fix client-only tags with RELAYMSG.

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