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

Implements the new `CHATHISTORY LISTCORRESPONDENTS` API.

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

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

Fixes #1064.

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

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

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

Improve auditability of sensitive operator actions

strip local_ from oper capab names, also consolidate unban into ban

Give Tor clients who authenticate via SASL a unique cloak, so chanops
can ban *!*@tor-network.onion and still allow authenticated Tor users

HELP responses weren't taking the client nickname as a parameter,
as is standard.

Channel rename (both of registered and unregistered channels) would leave
the old name unreclaimable.

Fixes #1260

This didn't work correctly for IPv6 or custom nets.
/UNDLINE IP can temporarily be used to reset the throttle.

Tor listeners should never see an STS cap.

Add an undocumented 'hide-sts' key for listeners that hides the STS cap.
This can be used if the listener is secured at layer 3 or 4 (VPNs,
E2E mixnets). It will be necessary to add the relevant IPs to `secure-nets`.

Allow `JOIN 0` with a confirmation code

Record INVITE in DM history for the benefit of offline always-on clients

* Defer account login snomask until after connection registration is complete
* Don't send account-notify for pre-registration clients

Include an 'r' flag in RPL_WHOREPLY for registered nicks

Enhancements to NS SUSPEND, including stored metadata and the ability
to list suspensions

Address SETNAME UX problems reported by @KoraggKnightWolf in #oragono:

1. No feedback by default on success or failure
2. Multi-word realnames are not correctly interpreted by some clients