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

Improve auditability of sensitive operator actions

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

checkAlwaysOnExpirationNoMutex was respecting registered status, but
always-on clients were not considered registered at the time of the
initial check, so they were being created regardless of expiration.

Add the new utf8-only cap, disallow non-utf8 when websockets are enabled

enable the use of grouped nicks as account names for SASL,
if force-nick-equals-account is disabled

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.

Fixes #810

1. Consolidate PURGE and UNPURGE into subcommands
2. Add PURGE LIST
3. PURGE ADD now requires a confirmation code

Fixes #1294

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

Fixes #1260