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

INVITE playback (#1409) was buggy, due to the double use of (Item).Params[0]
for the channel name and the recipient nick. Stuff the channel name in
(Item).Message.Message instead.

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

Validate imported databases for confusable nicks